Go to User CP
http://img163.imageshack.us/img163/9752/usercp.gif
Scroll down to Setting & Options, Click on Change Username
http://img846.imageshack.us/img846/6...geusername.gif
Enter your new username, re-enter your new username for verification
http://img233.imageshack.us/img233/37/newusername.gif
Do not forget to save changes
http://img811.imageshack.us/img811/4194/savechanges.gif