However, for many, having an extra workjob in the evening enlargincreases their incomes.

You can't say "having an extra work" because "work" is an uncountable noun. But you could say "having extra work". Read about it here:
https://www.englishclub.com/grammar/nouns-countable-un.htm

I changed "enlarges" because I usually hear that word used in terms of increasing physical size. For example, "enlarging a house".

ItThis practice becomes more common as our needs grow, along with the fact howevolve, and as new technologies change the structure of the modern society.

I changed the opening few words of your sentence because I think it's more academic to use a turn of phrase that makes it more explicit what you're referring to.

We don't need an article for "modern society". I changed a few other things to maintain tonal consistency, and because "the fact how" is ungrammatical. If you want to maintain that sort of construction, you'd say "the fact THAT new technologies are changing the structure of modern society." You could also say that technology is modernising society, or that society is becoming modernised by technology.

The question is w, "What are positive and negative effects in termsof this practice, ofn people’s lives.?"

Questions require a question mark. Often you'll put a question in speech marks, or parentheses in order to make the question (which is generally the topic or sub-topic of your work) distinct from the rest of your essay.

"in terms of" is redundant, mainly because when you use "in terms of" it really suggests that you're going to make it clear what those terms are, and actually both of our sentences (because I don't know what the scope of your inquiry is) don't go into much detail about how you'll be defining these positive and negative affects on people's lives.

It would make your essay stronger if you defined some areas of focus for determining the positive and negative affects of working two or more jobs, and switching between different career paths across the course of a lifetime.

For instance:

.impact on time spent with friends and family
.impact on mental health
.impact on level of income
.impact on self reported quality of life
.self reported level of work life satisfaction
.impacts on physical health

Let’s start by looking at the advantages of working in more than one jobs.¶
¶

It's ungrammatical to refer to "more than one jobs", because "jobs" is a plural noun, and "more than one" already indicates plurality.

You also don't need the preposition "in". It's redundant, but it's not necessarily wrong.

The main benefit tof work more, obviously,ing a greater number of hours is to earn more money.

There's no need to say "obviously", because it suggests either that the reader is a bit dumb, or that it's something so obvious you needn't have written it. It's better to just let your statement stand on its own merits, and if it's obvious then that's ok.

However, for many, having an extra work in the evening enlarges their incomes.

The word "an" is redundant. One might refer to "an extra job", or I might talk about "my work", but it's not actually synonymous with the word "job".

In both occasioninstances, this afford people the opportunity to improve the quality of their lives by purchasing better quality goods.

In English we say "on" occasions" but we say "in" instances.

I love your usage of the word "affords". It's a little antiquated, but it's a nice bit of flair. When one uses the term "affords" it's important to mention which thing is being afforded and by what. In this case you've explained what's doing the affording, or the giving of the opportunity, but what's actually being afforded is an opportunity.

You could also just say "allows". "This allows people the opportunity to improve the quality of their lives by purchasing better quality goods".

Turning to the other side of the argumenBy contrast, having more than one job can causes stresses and anxiety.

There's no guarantee that having more than one job will definitely cause stress and anxiety, so it's better to write that it's a possibility than that it's a certainty.

By contrast sounds a bit more natural, or you could also use an idiomatic phrase such as "Playing devil's advocate".

Moreover, itstress and anxiety makes people vulnerable to aill kinds of diseases due toness and disease, by impairing of their immune system.s.¶

I'd be really clear about how it makes people vulnerable to disease/illness, because the link might be obvious to you, but not to the reader.

I suggested that the link was stress and anxiety, but you could also mention factors such as the role of sleep deprivation in immune system impairment.

Another major drawback is a breakdown ipotential drawback of working more than one job, is its effect on familiesy life.

You need to make it clear what the drawback you've mentioned is a drawback of.

If you want to keep your sentence much as it was, you could say "the breakdown OF families".

Generally speaking, this situation disrupts relationships insidewithin the family thatunit; which could even lead to the divorce.

You don't require an article there for "divorce", it's just
"divorce", not "the divorce".

I used a semi-colon to indicate two separate ideas within the same sentence which aren't necessarily connected by the sentence's initial premise.

For changing a career, oOne of the main reasons for changing a career is to find one’'s place in life.

I just made a few minor syntactical (word order) changes here, and changed a couple of words around to make it more natural.

People who decide to change their career, may face the situation of being a novice in their new career, but obtaining thmore desirabled work can bring a new sense of meaning to their lives.

If you're talking about a new sense of something, you need to say what that something is.

Similarly, if you're talking about being a novice, even though it is implied by context what you mean, you need to say what it is they're a novice in.

WUltimately, however, working in more than one job, however, introduces more problems that, in many cases don’, aren't worth it.

This conclusion doesn't feel conclusive enough. I added the word "ultimately", because otherwise it seems like you're going to continue to explain yourself in another paragraph.

ItThis is becomesing more common as our needs grow, along with the fact hownd new technologies change the structure of the modern society.

The question is, what are the positive and negative effects in termthat this has ofn people’s lives.?

The main benefit tof working more, obviously, is to earning more money.

However, for many, having an extra workjob in the evenings is simply to enlarges their incomes.

Add simply to show that they don't necessarily need the money

In both occasions, this affords people the ability to improve the quality of their lives by purchasing better goods.

Turning toOn the other side of the argumenthand, having more than one job causes stresses and anxiety.

Moreover, it makes people vulnerable to all kinds of diseases due tobecause stress can impairing of the immune system.

For changing a career, one of the main reasonsOne of the main reasons for changing a career is to find one’s place in life.

In some cases, it may add value and meaning, to life; however, starting from scratch all the time can be frustrating.

ToIn concludesion, changing one’s career or working in several jobs is never easy.

People who decide to change their career face the situation of being a novice but obtaining theone's desired workcareer can bring a new sensemeaning to their lives.

Working in more than one job, however, introduces morenew problems that in many cases don’t worth outweigh the benefits.

It becomesThis phenomena is becoming more common as our needs grow, along with the fact hownd as new technologies change the structure of the modern society.

The question is, what are positive and negative effects in terms of(that this way of living has) on people’'s lives.?

The part in parentheses can be omitted, but the sentence feels a little empty and less academic to me without specifying the subject of the embedded question.

Let’s start by looking at the advantages of working in more than one jobs.

"Working a job" is a common and useful expression!

The main benefit to working more, obviously, is to is earning more money.

In essays, you typically want to avoid words like "obviously" because the point is to build your arguments and present facts to an audience that might not think your way of thinking is so obvious.

However, for many, having an extra workjob in the evening enlargincreases their incomes.

In both occasiones, this affordcan help people to improve their quality of their lives bylife by enabling them to purchasinge better goods.

Turning toOn the other side of the argumenthand, having more than one job causes stresses and anxiety.

Your transitional phrase here was a bit too long and bulky. It's best to stick with a set of a few "standard" transitional phrases that as well-used and established in essays.

Moreover, it makes people vulnerable to all kinds of diseases due to impairingment of the immune system (caused by stress).

I added "caused by stress" in there because working a second job isn't in itself what causes the immune system to be weakened.

Another major (potential) drawback is afamily breakdown in families.

I slipped "potential" in there because family breakdown is not 100% a given in cases where someone is working more than one job. It's good to sort of limit broad claims and statements.

Generally speaking, this situation disrupts family relationships inside the family thatand could even lead to the divorce.

For changing a career, one of the main reasons isConcerning making career changes, people often do so to find one’stheir place in life.

In some cases, itchanging careers may add value and meaning, to one's life; however, starting from scratch all the time can be frustrating.

To conclude, changing one’s career or working in several jobs is never easy.

People who decide to change their career face the situation of being a novice, but obtaining theone's desired work can bring a new sense (of achievement? A sense of what?) to their lives.

Working in more than one job, however, introduces more problems that in many cases don’tn it is worth it.