Unfortunately, it's not possible to change your username, both on the forum and in-game. We used to have an option to change your forum nickname (what your name will show as on the forum) but we had to remove it while our website goes through a renovation. We're not certain whether or not we will be bringing back the option to change your nickname, but hopefully we will look into it at some point. The only way to change your username would be to create a new account when the Registration is open. Hopefully this clears it up. c:
