It's really easy depending on whether you're on a PC, laptop or device. You just click on your profile and then click " Edit" profile. Then take off the name you first put in and the name you want in. Then make sure you click to save or update your profile and your name will come up as the one you wanted.
Hi Musical! To change your username, go to your profile, type in a new first name, a new last name, then press update, that should change it for you!