To change the main domain on your cPanel account please contact support at :

http://support.ifastnet.com

And ask us to change the main domain for you (please ensure that the new main domain name is NOT added to the cPanel at that point ).

Note if you change your domain name often scripts such as WordPress require the domain to be changed in the wordpress db or scripts configuration file BEFORE the main domain is change in cPanel, so ensure you make the appropriate changes to your scripts site url settings before requesting a main domain change.