You can change the hostname of your Dedicated Server through your Plesk Control Panel. This will change the hostname of your server within the Plesk environment only. In order to update the hostname that your server's IP address resolves to on a DNS level, you will need to request a PTR DNS Record (Reverse DNS Record) setup for your server's IP address. 

I. How to update the hostname within your Plesk Environment:

1. Login to your Plesk Control panel using your administrative access. 

2. Click on Server from the navigation bar on the left

3. Click the Server Preferences icon.

4. Enter the domain name / hostname you'd like to set for your dedicated server using the Full hostname text field

5. Click Ok to apply the change.

II. How to change a PTR DNS Record for your server's IP address:

What is PTR Record: Pointer Record or also called a reverse record. A PTR record associates an IP address with a hostname. PTR records should point to a name that can be resolved back to the IP address. A single IP address can only resolve into a single hostname, unlike hostnames which can resolve to multiple IP addresses.

If you'd like to change the default PTR Record for your server's IP address, please log into your http://serverportal.com account.

• Select “Billing and Services” then “View Services” on the left side of the screen

• Select the server that has the IP that you want to change the rDNS for

• You will now be able to see the information about your server.
• You will need to edit the NetFlow Primary or the Netflow (if you have a secondary IP on the server) in order to set the rDNS

• Save your changes to make them effective.
• Please note that this domain name should be already hosted on your dedicated server.