What should I buy to upgrade from 8.1 to 8.1 Pro

Hello, I need to upgrade my Windows 8.1 to the professional edition. But I really don't know what to buy: http://puu.sh/bWCsv/8d27f9a775.png http://puu.sh/bWCtd/27150b33c3.png I can choose between these 2 products. I really want to keep my files on my Windows 8.1 while upgrading to the professional version, will this be a problem or not? And should I do a backup just to be sure? Thanks...