I have a client who recently wanted to get a Windows 10 Pro PC for >their office. He went to Best Buy but all they had was Home edition. This is not an issue since you can upgrade Home to Pro with a simple license key upgrade. But it turned out that when I went to install the new key, I got an error. Nice! Follow MS’s procedure and get an error…..
BUT, I was able to track down this solution. Install a temp license key that will allow the actual upgrade to work, THEN install the newly purchased key.
VK7JG-NPHTM-C97JM-9MPGT-3V66T – Install this key first, Reboot, then install the key that you purchased.
support.microsoft.com/en-us/help/12384/windows-10-upgrading-home-to-pro – This is where you go, but you have to install the temp key first, then the correct one.