I suggest you next uninstall your existing version and try to install from just the update. You should not need the previous version installed.
Personally I would also clean my registry with Ccleaner after uninstalling. That carries some risk and an image backup of your system drive is recommended first (e.g. using Macrium, Acronis TrueImage etc.), or at least set a Windows System Restore point. Backup your registry when Ccleaner prompts you to.
So it is now solved but I'm not sure why. I rebooted, and then used Edge instead of FIrefox as my browser to download it. I seem to be having some flaky results with Firefox lately, so maybe that was it or maybe it was just gremlins. Thanks for all the suggestions. Sometimes technical problems are very frustrating and when it works you still don't know why.