1, Open a command prompt with elevated rights

* Hover mouse in the bottom left hand corner to get the start icon or use ctrl+esc or windows key / command key.
* Right click anywhere on blank space in the start launch or ctrl+tab.
* From the Apps launch start typing “CMD” then right click or arrow key til highlighted and alt+spacebar to get the options to run as administrator.

2, Type the following command to register key

Type:
“slmgr.vbs /ipk {product key, including dashes}”
hit enter

Below is a Video showing you what you need to do: