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.
How Do You Change Your Username On Weeworld?
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 !