With you have done the upgrading process and your Windows is activated
You can use advanced recovery to do a clean installation to remember you need your content and DVD or flash drive ISO
https://www.microsoft.com/en-us/software-download/windows10
If anybody does try it and it does work please do tell us
But with your like me and just want to do a clean installation any time if anything goes wrong
then here is the answer to get your key after upgrading Windows 10
Make sure your new windows is activated first
Go to this website and they will explain how to do it and other things
http://www.forbes.com/sites/antonyleather/2015/07/30/windows-10-updating-reinstalling-and-activation-guide-essential-advice-to-avoid-problems/