You can change your server’s hostname in WHM by browsing to:
Networking Configuration —> Hostname

Note: It is important to choose a hostname that you will not be using for any account. Your hostname must be a Fully Qualified Domain Name. In English, a hostname should consist of a name and a domain name. All valid hostnames should have 2 dots in them. Hostnames should never begin with “www”. Hostnames should also not begin with a digit, nor end with a hyphen (“-“).