I can not remember the root password to my Webmin. How can I recover or change it?
Well, that would be the same as your root password in order to log into your Linux box, whether at the console, over SSH, or via Webmin.
It would have been set during the initial installation of the operating system.
That doesn't by chance help, does it? :-)
If you lose your Linux root password, you'd have to boot into single user mode while at the console in order to reset it -- how exactly to do that depends on what distro you're using.