You have to have a valid reason to get it changed. I think the only reason you can request a new one, is if your real name is in the username.
Add me peacelvr15
You can't....
You can't
Yuh Can't Once Yuh Make One..Wen your Finish Makiin A Wee Mee Iht Says >>*+*Are Yuh Sure Yuh Want This Username.? *+*
You Go to Settings on the top right !