Change The Name Of System?

I recently purchased a new computer and my son registered it or did something under my name after building it. I tried changing the username and the computer name but it still shows files with my name attached to them. Call me over protective but I was taught when I first started using computers that you should not have your name attached to them. I don't want someone hacking into my computer and knowing anything about me. It pains me to see my name right in front of my face knowing someone could use it in some way.When I search my name in the search box it brings up a folder with a Lock on it. Inside the folder is a group of folders. These folders say things such as contacts, desktop, downloads, favorites, links, my documents, my music, my pictures, my videos, saved games, searches