I used to play piano, forom elementary school to high school, but I totally can'tforgot how to play piano now since I haven't played for while. I used to play piano, from elementary school to high school, but I totally forgot how to play piano since I haven't played for while.

Describing a duration: from X to Y

I used to play piano forom elementary school to high school, but I totally can't play piano nowthese days, since I haven't played for a while. I used to play piano from elementary school to high school, but I totally can't play piano these days, since I haven't played for a while.

An idiomatic replacement for "I haven't played for a while" is "I'm out of practice", should you prefer to use it instead.

I used to play piano forom elementary school to high school, but I totally can't play piano at all now since I haven't played for while. I used to play piano from elementary school to high school, but I can't play piano at all now since I haven't played for while.

"totally" is normally not used in a negative context. "can't X at all" is more standard.

I used to play piano forom elementary school to high school, but I totally can't play piano nowanymore since I haven't played for while. I used to play piano from elementary school to high school, but I totally can't play piano anymore since I haven't played for while.

I used to play the piano forom elementary school to high school, but I totally can't play piano now since I haven't played for while. I used to play the piano from elementary school to high school, but I can't play piano now since I haven't played for while.

I can readstill read (sheet) music though. I can still read (sheet) music though.

I would add "still" as emphasis since you are talking about how you retained some of your skills This "language" of music notes is referred to as sheet music

I can read musical notation, though. I can read musical notation, though.

Plain "music" is okay, but "musical notation" is more definite, especially if you're talking about stuff like staves, clefs, and notes.

I'd really like to practice piano again, and willto be able to play La Campanella that was made by Franz Liszt someday. I'd really like to practice piano again, and to be able to play La Campanella by Franz Liszt someday.

You can say "I'd really like to practice..." but "I'd really like to will be..." is not grammatically correct. Removing the "will" makes it work

I'd really like to practiclay the piano again, and willto be able to play La Campanella that was made by Franz LisztFranz Liszt's "La Campanella" someday. I'd really like to play the piano again, and to be able to play Franz Liszt's "La Campanella" someday.

Titles of works are best indicated by enclosing them in quotation marks; but, if you are writing in something that supports fancy formatting, you can italicize titles instead.

I'd really like to practice piano again, and willhope to be able to play La Campanella that was made by Franz Liszt someday. I'd really like to practice piano again, and hope to be able to play La Campanella that was made by Franz Liszt someday.

"will be able to" is a very definite statement, but the first part of the sentence "I'd like to" is much less definite, so it doesn't really fit.

I'd really like to practice piano again, and will be abl. I’d love to play La Campanella that was made by Franz Liszt someday. I'd really like to practice piano again. I’d love to play La Campanella by Franz Liszt someday.

I'd really like to practice the piano again, and willsomeday be able to play La Campanella that was madewritten by Franz Liszt someday. I'd really like to practice the piano again and someday be able to play La Campanella that was written by Franz Liszt.