how to change computers name?

The computers name is found in System Preferences - Sharing - Computer Name at the top.

I also think you might be referring to the home folder, is that correct? If so then the best option would be to create a new user for yourself ( System Preferences - Accounts - +). There is a method of manually changing it however it is not really recommended and can easily be screwed up.

 

If you just got it, I suggest you do a clean install of software. After it restarts, it'll ask you for name, network, etc.

You don't really want someone else's identity or settings on your machine anyway.