I was just wondering how I can change the computer short name in accounts and the wireless network name of my computer because right now it still shows the name of the previous user that I got the computer from
Here's an application I've used in the past to change my short name. It worked great for me. Be careful, though, because this is no light task. The program just makes it look that way.
They didn't, it's just the nature of *nix. Your short name is referenced in many places, namely the password file and such so if you change it in one place you have to change it everywhere which to the average user is no easy task.