You can't change ur USER NAME by yourself. To change USER NAME first create a new account with your desired name. Then you have to inform moderation team to move your all sites on your new user name. You also have to inform them the reason why you want to change your user name and don't forget to write them your old user name, old password, old mail address, new user name, password.
But there has 98% chance that you won't get their reply.
Its because moderation usually avoid this kind of request. Generally they don't want to give this facility to users. Unless someone able to impress them showing some good cause.
If they feel interested to help you in taking new USER NAME then they will inform you on your MAIL ID. So, always use valid MAIL ID.
