To change your username, follow these steps:
- Enter Menu and then Settings
- In the Account section, click on your username
- There you will see your current username; if you tap on it you can enter a new one
- Finally, tap save and your new username will be registered
Keep in mind that the username must be unique, that is, it cannot be being used by another user.
If the one you want to add is already in use, try adding a number to the end.