Ask Simon. He is the only one who can change it for you. When I was changing my name he asked for a few requirements. (These were directly from my conversation from him):

• It will only ever be done once.
• You must have a good reason for the change.
• Choose an appropriate username.

Don't be suprised if he doesnt reply straight away, I'm sure he is busy :) So just wait it out and chill.

~Wazabi