how do I get icloud on my mac?

I have both an iPhone 5 and Ipad mini which both use iCloud and which I find great as my photos are shared between the both. I also have a Mac Book so thought I'd take the plunge and set it up on there too. However, it doesn't appear in the System Preferences. I have a MacBook Pro running Max OS X 10.6.8 and from viewing some documents on the Apple Website it says to go into System Preferences, and set up iCloud from under the Internet & Wireless section. The trouble is, I only have an option for MobileMe (which I am assuming has now been replaced by iCloud?). Can anyone tell me how I get 'MobileMe' updated, or get iCloud on my Mac please? Many thanks.