Currently Being ModeratedFeb 9, 2013 12:28 PM (in response to G.Laurenceau)
First you will need to upgrade to Snow Leopard and then update Snow Leopard to 10.6.8.
Then check to see if your computer meets the requirements for Mountain Lion.
Then check application compatibility.
If there are applications you want to keep using that aren't compatible, you can always keep Snow Leopard on a second partition.