I could update VMware Fusion 7.1.2 virtualized Windows 7 Home Premium OEM 32-bit VM to Windows 10 64-bit the following way (I wanted to keep my old Windows 7 so I duplicated the old VM):
1. Duplicate the old Windows 7 32-bit VM.vmwarevm. Launch the duplicate in VMware and choose "I moved it" so it AFAIK preserves its VM's hardware info as opposed to the "I copied it" option.
2. Update the Windows 7 32-bit VM duplicate to Windows 10 via a mounted Windows 10 32-bit installer .iso. The installed Windows 10 activates with the "moved" VM hardware info.
(I could have now skipped to step #3 right away but I first unsuccesfully tried to install Windows 10 to a brand-new VM which didn't activate because AFAIK the new VM hardware info was different. So I again duplicated the old Windows 7 32-bit VM, launched it and told VMware that "I moved it". Confirmed that the duplicate VM was still activated to Windows 7 Home 32-bit.)
Now the now-obvious trick that did it:
3. Shutdown the VM that was activated in Windows 7 and now also in Windows 10. Attach a Windows 7 64-bit Windows.iso installer to it as a DVD, and set the VM to boot from that. Boot the VM into that Windows.iso installer (I had to reboot VMware because the 1st boot stalled).
Now, let the Windows 10 64-bit installer REFORMAT the old Windows 7 virtual HD. When the setup is ready, the cleanly installed Windows 10 64-bit should be activated!
(One option is to delete the old VM HD and create a completely new, but I don't know if it had been considered "too much new HW" to be activated. In fact, I first tried this but the Windows 10 install "express settings" got into an endless loop then.)
I installed VMware tools and confirmed that the OS was activated also after that.
As a final step I changed VMware settings > General the VM's name and OS to Windows 10 x64.vmwarevm from the old Windows 7 and Windows 10 remained activated after that, too.
Hmm, maybe I should keep a copy of a VM-HD-reformatted Windows 7 & 10 activated VM in a safe place. Reformatted and optimized, it is only 111 MB.
I wonder how I can set VMware VM HW settings to match those that activate my copy of Windows 7 and 10.
