After you install WordPress, it states that once you select a username, that it can not be changed later; yeah right.. There is a plugin for Username Changer, that really is not necessary to even install.. You can do this in two easy steps.
It’s best security practice to use a different username & nickname, than the generic ‘admin’ provided during install.
So, here is how you change the username after you install WordPress..
Access your phpMyAdmin, select the WordPress database find ‘table_user’ and select edit and change to your unique name, then save.
Log back into your WordPress with your new user name.
There are other methods and plugins that will change WordPress username; check out the resource section for more information. Personally, the less plugins the better!
How can I change my default WordPress Admin Username: http://www.websitedefender.com/faq/change-default-wordpress-admin-username/
WordPress Change User Name: http://wordpress.org/support/topic/change-user-name