Username is never changeable.  So no one in this forum can change his username. But the display name can be changed but the forum only allows him to change the display name of his account who has enough reputation in this forum and who is known by most of the people in this forum.  So with your account situation I don't think you can get that chance.

So if you are not satisfied with the current name, you can open a new account with the name of your choice. Because this forum will allow you to use two or more accounts if you have not committed any crime.