The Hostname is/was the Name of your Server. We used to put the domain name or the Server's entry point. However, It does not make much sense to many people now. It is because we/anyone does not manage domains on the Server with the Hostname.
However, If you need to change the Hostname for any reason, You can do it by following the step-by-step guide below.
Step 1: First, log in to the ServerAvatar Account.
Step 2: Click on the Server Dashboard button.
Step 3: Now, you will see the option Settings on the left-hand sidebar of the Server Panel. Click on Settings.
Step 4: Now, you will see the Settings form like the below image.
Step 5: You can change your Hostname, Then click on the Update button.