Before anything I should acknowledge that my question was not understandable enough. So I totally edited that
I have a VPS with DirectAdmin control panel.
One of my users had registered with domain1.com. Now he had decided to change his domain. That's all he is going to do. NO files, databases, username, email accounts are changed. The only change is the with the domain name.
Is there a way to change an account's primary domain name in DirectAdmin?