How do I change the User/library name on snow leopard?

My dad gave me his macbook and it's got his name on the user on the side panel and I want my name there instead. I know how to change the login name etc. but I can't figure out how to get past step 9 of http://support.apple.com/kb/ht1528 (enabling root user) I can't choose enable root user from the edit menu as it doesn't show.

I'm new to macbooks so it would be great if someone could explain it so that I'd understand 🙂

Thank you.