Yea, what he said! From the posted link:
1) How do I change my username?
The site owner, Mr. Lindsay Blanton, is the only person who may do this. You must email him privately at webmaster @ radioreference.com. Be ready to give a good reason why it needs to be changed. Generally usernames are changed because of an amateur radio callsign grant - or change - or you later decide your username should have not contained your true name. All else will undoubtedly be denied.
Since you specify that your decision to change usernames is due to it "should have not contained your true name" you probably have a good chance to get the change approved. Regardless, it's up to the site owner to approve or reject the request.