How do you upgrade to 18.10 from disk?

So I have this Kubuntu VM installed ... unfortunately, I never bothered to install updates.

That wasn't an issue until recently, when I needed to get some new packages and just couldn't.

So I went online and turns out, I still have 17.04 ... whose directories have been taken down.

How do I upgrade from disk? I remember earlier ubuntu derivates gave you the option to when you put in a boot disk, but this time, it's just "Try 18.10" or "Install 18.10".

The VM took some time to set up and there's some data on it that should be properly backed up but I've been too paranoid to actually delete. (Most of my data is in shared folders with the windows host, anyway, but in this particular instance, I had run into permission issues with the files, so I moved them to VM memory.)

So I'd really hate to re-setup the whole thing. -.-

Is there an option to upgrade the running System from the iso?