Deleting a user?

So, here is my situation. I had an iBook G4 years ago. About 1 year ago, I got a MBP and I put all of my data onto my new computer. Then, my brother took my old iBook and put all of his music and stuff on there, but the accounts and stuff remained untouched. Recently, he got a new mac himself, and migrated all of his stuff from "my" iBook to the new mac. Consequently, in Finder above the "applications, music, etc" sidebars, is the sidebar/folder with MY username. Can this be changed and/or safely deleted? It says that that folder contains ~16GB of info (I assume that's basically all of the stuff that was transferred over)... but despite setting up his new mac under his account name, why does this folder (filed under Macintosh HD --> users) report me as the username and will not allow me to change it when I go to "get info"?

Sorry if this was unclear at any point, please say so and I will gladly clarify!