Transfer a Windows 10 license to a new PC
The process was rather simple, but I could not find the solution anywhere on the internet. The process detailed on How to transfer a Windows 10 license to a new PC or hard drive did not helped me.
I contacted windows support and they told me that I can activate Windows 10 on my new PC using the Windows 8.1 key which I used to upgrade to Win 10; this worked for me after deactivating Windows 10 on older PC using slmgr /upk.