Q: how can i tell what is taking up most room on my hard drive?

Try a program such as Disk Inventory X or OmniDiskSweeper.

(57901)

I  installed Disk Inventory, and it tells me I have 169 GB under iTunes and another 334G under Users/Gus/Music/iTunes.  Isn't this the same stuff?  Isn't that why my disk is so full?  Can I get rid of the stuff under Users?

Ahh thank you for telling us bout Disk Inventory. I just read this posting. Very useful tools to know which is the most biggest application capacity.

Now I know. My Android Studio takes more than 60 GB