If you are just doing an update (not a clean install), all you have to do is double-click it. That's it.
It works regardless of what OS version you're on now (i.e. you don't have to upgrade to Yosemite first).
If you wanted to do a clean install, then there would be extra steps. But the package itself is designed as an update, not a clean install, so there's nothing special you need to do.