After moving server image Virtualmin password no longer works

I want to create a copy of a website under a different domain name. The domain names are related: the old was mydomain.net; the new one is mydomain,com.

So I made an image of the server and copied that (under DigitalOcean: create droplet from snapshot).

Now I want to access Virtualmin that is installed on the image, so that I can setup the server correctly. I get the login screen, but it doesn't accept my username/password combination.

I have two questions: - why does my Virtualmin password not work after this operation? - is there any way I change the password with FTP or the console?

Thanks. MM