The only way you can change your main charc name is to switch servers. Pick a server you want to switch to - create a mule on that server with your name - when you switch to that server via the World Pass option, you will be prompted to change your name - after you change your name, delete the mule that you created if you have no use for it.
But warning, once you have changed to the new server, you will not be able to switch right back to your old server. You have to wait 90 days between transfers and pay the World Pass fee again.
The only other way I know if changing a name is creating a new charc, name it and start from scratch. Since I have several 75 jobs and there have been some servers that had people on it that I wanted nothing to do with, the changing servers option was very attractive to me. I managed to move, leave behind those losers and make new friends on a new server.