Upgrade Help El Cap to Catalina ?

I currently have a working (for a few years now) dual boot with a single hard drive an El Capitan and Windows 10 system.
With today's apps, I need to upgrade to a more modern Mac OS but try to retain the dual boot option without disrupting the Windows install.
Any MacOS will be ok for now if that is an easier option, otherwise, Catilina would probably be the best bet. The dual boot setup with the single hard drive was pretty difficult so I have been putting off a Mac OS upgrade/update.

Author: chippeto