There's no user ability to change username. But the site Admin may be able to do that for you; you can try sending a private message to the WWEnd Site Administrator.

Welcome to Worlds Without End! You might try reading our newly-updated FAQ to see what sorts of features you can explore, and people are always willing to answer questions in the Forums.  

Also, you can access your profile by clicking "My World" in the top-row menu (or by clicking on it anywhere it's hyperlinked, for instance in your post above this one).