Você vai querer seguir o procedimento Adicionar recursos ao Windows , conforme descrito no site do Windows .
Add Windows 8 Pro Pack or Windows 8 Media Center Pack to your edition of Windows
Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, and then click Search.)
Enter add features in the search box, and then tap or click Settings .
Tap or click Add features to Windows 8 and then do one of the following:
If you need to purchase a product key, tap or click I want to buy a product key online.
Follow the steps to purchase and enter a product key.
If you already have a product key, tap or click I already have a product key.
Enter your product key and click Next.
Read the license terms, select the check box to accept the license terms, and then click Add features.
If you were running Windows 8, your PC will restart automatically and Windows 8 Pro With Media Center will be available for use.
If you were running Windows 8 Pro, your PC will restart automatically and Windows Media Center will be available for use.