If you wish to change your username, you'll first need to login to your profile. Once you've done that, follow these steps:
1. Click on the menu icon on the top right of the page (to the right of your picture).
2. A menu will appear. Choose the Heading that says 'Settings'.
3. Under My account settings click change next to Username to update this information. Your username can not be in use by another member, or contain any spaces or special characters (#*&%!).
4. Type in the new username you wish to use. Click change username when you're done.