When you try to change the product key in Windows 8 or in Windows Server 2012, you cannot find a “Change product key” link in the System item in Control Panel.
Use this to enable the “Change product key”
- 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 0x3.
- Tap or click the Slui.exe 0x3 icon.
- Type your product key in the Windows Activation window, and then click Activate.