As D-ead7Dog has already said, you need to visit the 'User Panel' and log in, then find the correct field to successfully change your username. This will also change your forum username so people can recognise you clearly and won't get confused.
Below, I've placed a small step-by-step tutorial and highlighted where you need to be looking and/or clicking!(http://i.imgur.com/5sKlhNT.png)
(http://i.imgur.com/Im1Tkux.png)
(http://i.imgur.com/OD56qW1.png)
If you come across any further issues, be sure to send an email to [email protected] using the email you've created the account with. Include your old username and the new username you'd like to change it to. Any other messages sent through, such as "hello c:" or whatnot, will not receive a response.