Bill what is your joomla version? If you don't see it in the update manager, then maybe you are running an old joomla version?

3.6.4

Strange. Then try a normal update through the extnesion manager. It should work.

Regards,
Daniel

It reports
Update: Could not open update site #14 "CMC Updates", URL: https://compojoom.com/index.php?option=com_ars&view=update&task=stream&format=xml&id=13&dummy=extension.xml
Maybe the same problem that was preventing Install from Web on my other website (which was a clean install, no prior CMC)?

There are servers that for reasons beyond my understanding are unable to open the url above. As you can see the URL can be opened in a browser and there is no issue with the certificate. But on some joomla installations that doesn't work and you seem to be on one of those servers.

Did you manage to upgrade it manually?

No, I couldn't find any manual upgrade process while searching, so didn't want to do it wrong and lose my current install and setting. Do I just install the 3.01 zip like normal and it will see the 2.0 version and replace it?

Exactly. Just install 3.0.1 over and it should be fine. You shouldn't lose any settings. (as usual though - make a backup before performing the update)