You already have Snow Leopard (10.6.8). :Lion is 10.7 and Mountain Lion is 10.8.
Lion (10.7) is no longer readily available, so your goal should be to upgrade to Mountain Lion (10.8). The easiest way to find out if your Mac meets the requirements is to open the Mac App Store and attempt to purchase Mountain Lion. If your machine doesn’t meet the requirements, it won’t let you complete the purchase.
