Add Windows 8 Pro Pack or Windows 8 Media Center Pack to your edition of Window
1. 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.)
2. Enter add features in the search box, and then tap or click Settings .
3. Tap or click Add features to Windows 8 and then do one of the following:
3-1. If you need to purchase a product key, tap or click I want to buy a product key online.
3-2. You will be prompted through the steps to buy a product key from there and it will be entered for you.
If you already have a product key, tap or click I already have a product key.
4. Enter your product key and click Next.
5. Read the license terms, select the check box to accept the license terms, and then click Add features.
If you want to enable Windows 8 Media Center use the below product key:
More: Windows 8 product keys