I have an iMac with Intel i7 CPU and 32GB of RAM. 16GB RAM assigned to my Windows VM. I've followed the instructions on the knowledgebase to download the MediaCreationToolx64 application and select to do the upgrade. It does some downloading, eventually reboots the VM at which point it takes over my mac entirely full screen with no way of swiping back to the Mac OS screen. I get a blue screen with a language selection on it and a few moments later it just hangs. Now the mac is completely unresponsive and I have to hard-reboot it. Any ideas?
I had very similar problems, albeit with not quite as much physical RAM as you have. It all worked fine after I'd read a thread on here that recommended selecting the option to create media for later installation on another PC. https://forum.parallels.com/threads/what-i-learned-in-installing-win-10-under-parallels.329225/
I've tried the following.... Upgrade via tray icon - Fails due to display driver Upgrade using downloaded ISO - fails with "The installation failed in the SAFE_OS phase with an error during APPLY_IMAGE operation" Upgrade using media creation tool "Upgrade this PC now" option - gets to end of verifying download and simply quits without explaination. Upgrade using media creation tool to generate an ISO - fails with "The installation failed in the SAFE_OS phase with an error during APPLY_IMAGE operation" The two ISO options get as far as the black screen with the circle but at that point they ALWAYS completely lock up the entire iMac. Eventually causing it to reboot due to a problem. When the VM fires up again I see the "The installation failed in the SAFE_OS phase with an error during APPLY_IMAGE operation" error. Rapidly losing the will to live here and certainly don't intend on paying for PD11 given the number of problems reported on these forums with that and windows 10 also. Next attempt will be to remove Parallels Tools and re-attempt the upgrade. Failing that I will try a full reinstall of Win 8.1 clean from my retail media followed by an immediate upgrade to Win 10. If that all fails then I guess Parallels just isn't going to work and I'm going to have to look at other options.
Ok, tried removing parallels tools and running the update from the media creation tool again. This time it got to aboout 18% on the circle before my mac rebooted and it restored the previous version of the OS ... getting nowhere >.<