No Webmin / Virtualmin updates

My Webmin / Virtualmin has not shown any updates for a long time. I’ve had software and other updates to the underlying Ubuntu server as expected, but my Webmin / Virtualmin install is now several versions behind the latest release.

I’m fairly sure i had update notifications some time ago, so I can only assume that some file has been overwritten and now the relevant repos have been removed from my system.

Can, I just add in the relevant repos and my system will update without issue?
If so, what are the repos and how do I add them to my Ubuntu 14.04 server?

If not, how can I update/upgrade?