How to not get my cousins messages?

So I updated my iPhone to iOS 6 finally lol so I don't know what I did I just wanted to be over with but now I receive my cousins messanges we share the same apple account because I didn't want to get one so I tried Turing off ICloud but I still recive his text messages help please! Don't know what to do I use his apple I'd but don't know how to retore it to not get his messages

See if there's a default feature and a call blocking one, too.