I have OS X 10.5.8 and I need to upgrade

Hello everyone!

I need help. I have an iMac 2009 with OS X 10.5.8 and I need to upgrade, but I'm confused. Do I have to install Mac OS X 10.6 Snow Leopard and then install the rest so that I can finally install Mountain Lion?

And, should I save my pictures and videos on a backup in case they get deleted when I install the new OS?

Thanks :)