Why and how to change the default administrator username after installing Joomla
In the Joomla installation process the default account that is created is the Super Administrator account, which is called admin. In the final stage of the Joomla installation process you set the password, but leaving the username in the well known default admin value you expose half of your account's security.
We suggest you to change the default username of the Super Administrator account to something harder and more difficult to guess than the public admin name. This way your account security will be increased substantially.
It is very simple to change the username. First you will have to connect to the Joomla control panel and navigate to the User Manager menu. Then select the record of the admin user and change the value of the username field. A hard username is considered the one that contains letters and numbers. Finally click the Save button to save your changes.