for a macbook air 2012, a utility to clean up hard drive?

Hi, i have a 13inch macbook air from 2012 and my 120 GB of hard drive space is getting eaten up fast.
When i look at the storage capacity in System Information, I have this "other" category eating up 55gb of space. I don't know what that 55gb is, but I am ready to offload the 35gb of music i have onto a flash drive to free up that space, but how can i determine what is in that nebulous yellow bar of "other" and maybe clean it up a little.
I am experiencing just a general slow down in my browser speed, etc.

thank you.

Before doing anything make sure you have a working backup of your system.

Look into the downloads folder and delete/move to external strage anything you no longer have need of.
Next get Onyx (for whichever version of OSX you have). Install and run everything on the automation tab.
This will clear out many caches and temp files that may have accumulated on your system. Please feel free to research this software on this forum and elsewhere so that you're happy about what it does.