This tutorial will teach you how to change the default Admin's Username in Joomla. You need to be logged in to your Joomla account, and at your admin panel. From the menu at the top left, select and click on Site. Now from the drop-down, click on User Manager.
This will open the User Manager screen. Check the box next to the administrator. Scroll right, and click on Edit in the upper right corner. This will open a User Edit window. The left hand box is User Details. Simply enter a new name in the Username field. You can also change the password. When you are done, click Save in the upper right corner. The screen will now verify that the changes were successfully saved. On the User Manager screen, you will be able to see the changed name in the Username column. This completes this tutorial. You now know how to change the admin username in Joomla.