Is it possible to change usernames? If yes, how?

It is possible to change your username. However this can only be done once per three months and at Angel's discretion. 

The link to the contact form is here: http://beastkeeper.com/contact-us

Angel has to manually change them, so it would not make sense to have users changing them all the time- that is why it is limited. 

Please see the FAQ's:

You can send a request through Contact Form. Please fill out this form and include it in your message:

Old username: Your old username
New username: New desired username
Reason: Reason why you want to change your username

I acknowledge that I won't be able to login with my old username once it is changed. I will use new username to access my account.

You can't request a username that is already used by another player.
You can request username change only once per 3 months with no special reason (like you just get bored with your username or don't like that it's all written in caps).

Thanks! That was helpful ^^ and I've changed my username!