Below mentioned are the steps to change the display name of admin user from PHPMyadmin. This needs the access to your phpmyadmin, and will make changes to your database values.
1) Login to your phpmyadmin.
2) Click on database.
3) Select your database from the list.
4) Search for the wp_user and click on the button shown in the figure.
5) You will find a list of users. Click on the pen button shown in the figure.
6) In the display_name field, change the value to anything that you want to display.
7) Click on Go.