Game username
Sadly you cannot change your game username. Ifyou really want/need to you would have to make a new account since both the game and site systems cannot change people's usernames. However, they can change forum names.
Forum name changing:
You know where it says 'Hello charlotte murray' ?
Below your picture, it will give you a few options. Home, help, search, profile, ect.
Select profile.
At the side in the 'modify profile' section there will be an option like 'account related settings'. Click it.
You will then see a box with the name charlotte murray in. type in your disired name.
Scroll down to the bottom of the page, write in your current password, and you're done. Rememeber that some names may be taken, so no good trying something really common.
Sorry for the terrible instructions cx If you want more info or a better explanation, please PM me. c: