Q: How to downgrade from OS X 10.8.2 to Mac OS X 10.7 on 2010 MacBook Pro

Hello all

I have a 17 inch MacBook Pro from mid 2010 and it came with snow leporad. In July 2011, I upgraded it to Lion and a year later to Mountain Lion. Mountain Lion has slowed down my computer somewhat. I would like to find out if it is possible to downgrade to at least 10.7 Lion. Lion shows up under the purchasses in the Mac App Store so I can still download it but how do I downgrade to Lion or snow lepoard? Snow lepoard was the OS that it came with but I would be fine either with Lion or Snow Lepoard