Cannot download Mountain Lion...

I bought this MacBook refurbished in early 2009, and I think this was made in 2008. I tried to download OS X Mountain Lion, and even though I already have 10.6.8 (or whatever the order of numbers are) it told me it's not compatible.

Please tell me that I don't have to buy another laptop just so I can have iCloud between my iPad, iPhone and MacBook...