This tutorial covers how to change a Virtual Server Owner's password from within Virtualmin.
It assumes you have first logged into Virtualmin.
Choose the domain for which you would like to change the password. You can do that by selecting the domain name from the drop-down box on the top-left.
Edit Virtual Server.
Administration password, click the radio button marked
In the text area next to
Set to, enter the new password.
Save Virtual Server.