We'll be happy to help you change your username! However, if you have created content for our site, remember that you might already have a following, and changing your username might confuse your followers or lose them completely.
If you want to proceed, simply submit a new ticket to our Support Center with a choice of 3 different usernames (in order of preference).
We'll always try to give you your first choice, but we're a big site, and usernames might be taken already so that we will try the next.