[Serghate]

Contact a member of the staff and request assistance with getting your username changed. If they cannot change it, at least they'll give you a correct answer on what you have to do to have the name you wish to change to. They sure can give you a better answer about this.
They might tell you to forward your request to someone in specific or through other means rather than a PM, costs nothing to ask, so why not!
Good luck!