I have a license for Windows 8.1 Pro 64-bit Retail, and I want to uprgade it to Win 10 while it's free, but the upgrading of the license doesn't seem to work. Here's what I did: - I installed Windows 8.1 Pro 64-bit in a virtual machine; - I activated Win 8.1 using the product key; activation worked; - I used a Windows 10 Pro 64-bit iso, to upgrade from Win 8.1 to Win 10; - after the upgrade completed, Win 10 was already activated (it seems that the Win 8.1 activation transferred to Win 10); - I deleted the virtual machine; - I created a new virtual machine, and I did a clean install of Win 10 Pro 64-bit in that new virtual machine; - after WIn 10 finished installing, I clicked on "change product key" to enter the Win 8.1 product key so that I can activate, but after entering the product key correctly, this error is returned: The product key activates win 8.1 pro, but it doesn't activate win 10 pro. The only way I could activate win 10 pro, is by activating win 8.1 and then upgrading to win 10 using a win 10 pro iso. This means I have to keep both a win 8.1 pro iso, and a win 10 iso, but I wanted to delete the 8.1 iso, and keep only the win 10 iso, because I will not use win 8.1. Is it possible to activate win 10 pro, with a win 8.1 product key, but without upgrading from 8.1, so that I can delete the 8.1 iso and be able to clean install win 10 in the future ?