Yes you can. Only ONCE though. Go to ''Contact us" at the bottom of the page and for the "Regarding" portion, click "Other" and within the message box, just state that you want to change your username, with the new username added, and boom you're done. Takes about 24hrs for them to confirm it and change it. :)
You can send a message to me, or to username GirlsAskGuys, or use Contact us.
When you send the message, please provide your new user name (and 3 alternates), and we will make the change. Please note that you are only permitted to change your username ONE time, so please choose your new username carefully!