Here's how to change the hostname for your VPS or Dedicated Server.

Go to your Client Area: https://my.tsohost.com/clientarea.php and follow these steps

Services -> My Services -> click on the green "Active" button -> Login to Server

In the account Dashboard, at the top of the page select Settings.

In the Server section, next to Hostname, click Change.

Enter the new hostname in the Server Hostname field, and then click Save. The hostname must meet the requirements before you can save it. After you save the changes, the new hostname appears in the Settings section.