Hey can I change my username?

Sure you can, you'll just need to send a total of 100k(100,000TC) to an admin/ninja(?) and tell that what you'd like your new username to be.
Also bear in mind that the username you want to have needs to either be unused or if it is already on an account, it would have to be inactive for 2-3years or more with no posts on it.

http://forum.toribash.com/showthread.php?t=343024
read the first part

Thanks Mystery. It's so expensive though. :P

well the alternative thing you can do is make a new account in hopes it won't be taken. if you want to make that one brown belt it's really cheap to buy qi boosters from the Torishop I believe. you only need about 500qi to be brown belt