I dont think you can, you would have to start up a whole new account.
Correct me if I am wrong.....
I did that and now I'm a clone!
read: "New Name Suggestion" on this forum (dated Mar. 09)... you won't have to backtrack far to find it... judging by the response, it would appear that you can't.
Actually, you can change your user name, but you need to submit this request through Customer Support. Please use the Contact Us link at the bottom of every page to submit your request.