This article will show you how to remove a domain off your reseller account. Please note that you will need to create a Backup of your content before you delete the account. 

Step 1. Log into Plesk account 

Step 2. Once logging into your account, Click on Domains 

Step 3. Choose the Domain from the list below by clicking on the box next to the domain 

Step 4. Once you have selected the Domain, Click on Remove