I would like to completly uninstall and reinstal the ubuntu system

I got this desktop from someone who did not want it anymore (don't know the exact specs). It already had 2 copies of ubuntu and a copy of windows 7. The reason why is that I was able to load ubuntu once and now it gets stuck at the ubuntu loading screen. I had this issue with the windows copy as well but I fixed it by removing a stick of ram ( I have no clue as to how the 2 relate to one another). The other reason would be that I need to get rid of the password and remove the user name and this is the easiest way I can think of. obviously I am new to ubuntu and linux, so any help will probably need lots of detail.
Thanks in advance.