Normally, you can't change it. However, if that is your real name (it sounds like it might be your first two initials and your last name) and you want to change it, try e-mailing a webmaster and say that using your real name has become a safety concern for you and that you would like to change it to just "A.J." or something. I assume that privacy/safety really is your concern, and that you aren't just suddenly wanting to change for the heck of it to something more "fun".
They may or may not alter it for you, but it's worth asking. I only suggest that because you've been a member since 2005 and you have a couple of hundred posts. If you were newer or had a really low post count, or if you hadn't used your real name, or if you just wanted something more "fun", I'd just say to create a new ID.