Upgrade from Snow Leopard
It'll become a little bit difficult to upgrade to Mavericks since it has been replaced by Yosemite now. You can in fact upgrade from Snow leopard directly to Yosemite. If you Mac supports Yosemite you'll have to upgrade to Yosemite or by using a DVD you might have a chance to make Mavericks working, but that is not supported or encouraged. And you'll need a DVD.

I encourage you to upgrade to Yosemite if you can. It's stable and works fine. If you still have software that doesn't support Yosemite than rather stay with Snow Leopard then upgrade to any new. But I see no reason to stay with Mavericks instead of Yosemite. Unless it's not supported anymore for your Mac. 

In order to update to Mavericks first be sure the you're running on the most recent version of Snow leopard, 10.6.8 +. To check if you're Mac is still supported for Yosemite you can check it: https://www.apple.com/osx/how-to-upgrade/
It also states how to update :)

Good luck