I'm a root on my pc (linux ubuntu 12.04.3). NEED HELP!

I am one of 2 roots on my pc with Linux ubuntu 12.04.3 OS. There is the actual root itself then me. Some how before I became a root my pc got loaded up by an outsode source with a bunch of crap. My disk usage is being loaded at a quick pace with unremoveable & unopenable files etc & I don't know where they're coming from. Anyway, I want to clean EVERYTHING from the system and do a clean install of Linux ubuntu 12.04.3 but the unmount option in the disk utility doesn't recognize me as a root (or owner) and doesn't let me unmount. How do I make my computer know that I have root permissions so that I can perform the necessary operation?