Microsoft: Change Product Key in Windows 8 or Windows Server 2012

The two methods below allow you to change the product key in Windows 8 and Windows Server 2012:

<< Method 1 >>
1.  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.
2.  In the search box, type Slui 3.

3.  Tap or click the Slui 3 icon.
4.  Type your product key in the Windows Activation window, and then click Activate.

<< Method 2 >>
1.  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.
2.  Type Command Prompt in the Search box.

3.  Right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.

4.  Run the following command at the elevated command prompt:
slmgr.vbs /ipk <Your product key>