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You have a Mid 2010 MacBook, which supports Mountain Lion.
First of all, if you are happy with Snow Leopard, keep it. You shouldn't have any problem upgrading, but there are a lot of applications that don't work in Lion and Mountain Lion, so it's important to check that they are supported before upgrading > http://www.roaringapps.com
If you have decided to upgrade to OS X Mountain Lion, open the App Store and purchase Mountain Lion. While it's being downloaded, make a backup of your files. When the download finishes, the Mountain Lion installer will appear, so follow the steps to upgrade to Mountain Lion