At one time it could be done but not now. This is under "Help" > "Account":
Can I change my username?
Unfortunately no. Recently we have changed our policy and do not allow username changes anymore. Username changes have been starting to become more and more popular and these changes have been creating confusions among users. So, no more username changes. Thank you for your understanding.
Unfortunately you can't any more and they are very strict about it. I have tried to ask to change my since the get-go, but they bluntly said no and I don't want to start over and I just lived with it. You're only xper 2 so it won't be bad to simply start over