Hello Michael Newton !

If you have the 10.0.0-RC1 version then it means you made this upgrade before UNA 10 release. Then you need to revert back this part from the betas upgrade manual:

the inc/classes/BxDolUpgrader.php again and add /beta/ to the URL like this:

protected $_sUrlVersionCheck = 'https://v.una.io/beta/';

The upgrade button should appear after this action.