Changing your username is a simple process, but please keep in mind that it can be performed only once.
Head to your Account Settings, and at the top of this menu, you will see the option to change your username. Once this is done, it will not be possible to change it again, so please check and double-check that you have written what you intended to.
Customer Support will be able to help you with future changes, but this will only be permitted to correct spelling or change a username after it has been reset by our moderators.