KMS keys for Windows can be found here: https://technet.microsoft.com/en-us/library/jj612867.aspx
AVMA keys for Windows can be found here: https://technet.microsoft.com/en-us/library/dn303421.aspx
Running winver.exe shows us I’m tunning the Evaluation version:
In an elevated prompt type the following line:
dism /online /set-edition:ServerStandard /productkey:WC2BQ-8NRM3-FDDYY-2BFGV-KHKQY /accepteula
The product key that is used here is the KMS key for Windows Server 2016 Standard Edition.
Reboot the server (it will reboot twice!).
Again, this is the KMS key for Windows Server 2016 Standard Edition.
After that, activate Windows by typing the following in an elevated prompt:
Of course, this will only work if you have a KMS host running on your network and have configured the KMS correctly.
Thanks Arjan Mensch