Windows 8 - "Add Features" button doesn't show

I want to install Media Center on my computer. I obtained a Product Key from Microsoft and am trying to follow their instructions, which are the same as an article posted here on TR (http://www.techrepublic.com/blog/window-on-windows/how-to-add-windows-media-center-to-windows-8/6395). However, I don't have an "Add Features" button. All I get when I search for Add Features, is the button to Turn On Windows Features. Why am I missing this? I have Windows 8 Pro 64-bit installed on my computer.