1. Use slmgr
- Open an elevated command prompt and type the following commands:
- slmgr -upk
This will remove the key first
- slmgr -ipk xyzyx-xyzyx-xyzyx-xyzyx-xyzyx
This will add your key. Of course replace the xyzyx-xyzyx with your own real key.
- Activate Windows (you will probably have popups already during this process)
2. Use slui.exe
- Swipe in from the right edge of the screen, and then tap Search. Or, if you are using a mouse, point to the lower-right corner of the screen, and then click Search.
- In the search box, type Slui.exe 0×3.
- Tap or click the Slui.exe 0×3 icon.
- Type your product key in the Windows Activation window, and then click Activate.
3. You can also use the Volume Activation Management Tool (VAMT) 3.0 to change the product key remotely, or if you want to change the product key on multiple computers.
The last two methods can be found referenced in this KB: http://support.microsoft.com/kb/2750773