I check the current edition that is Standard Trial Edition and is Unlicensed now.
Right-Click this Server name to select "Enter Product Key..." on the menu
Follow the wizard to key in Product Key
Finally, you will see the summary message with power shell command for registering Licence Key. If the information is right, please click "Finish" button now.
Reconfirm Server Edition and License Number, it did change to legal edition now.
It is very simply, isn't it?
