You cant change your AG Username. If you really want to have the username of your choice, I insist you make a new AG account with a new email address. Hope this helped.
You can request for it to be deleted by emailing support@armorgames.com, but that seems like a waste of time. Just abandon that account and create a new one if you want a different username.
I have some issues with the Profile Name changing idea...I get some people aren't fans of their username and want something better, but I think it might add some confusion.
Say a user (lets call him...User) is spamming and gets reported, but before a mod or admin is able to do something he changes his name (lets say to...NotUser). Since is was User that was spamming and not NotUser (technically) there isn't much they can do to that person
Then of course, a username is someone's identity. Let's say Ghost decides he wants to change his name...would we get a notification about this? Or just have to find out eventually that this new user posting in the community is actually the well known Ghost?
Ideas proposed and backed up by Cormyn were that the previous username(s) would be displayed on your profile for everyone to see.
Let's say someone is spamming, they change their username because they think that'll get mods off their tail, on their profile it'll display their previous username.
And let's say I change mine, it'll show "GhostOfMatrix" somewhere on my profile.
But of course we have no clue if those ideas are still being considered because those threads haven't been updated.