BackUp current version MainStage and Logic

Hi !

I really like new way installing apps from Apple - AppStore. But now i confused with one thing:

How can i backup current version of MainStage and Logic ?

I have not DMG's from AppleStore :/ (i can't found where i can get it)
But we all know about two sides of "update" - one caise when all ok, anoher - when all die.

I'm about second. How can i save my current MainStage and Logic ? What folders i need to save ? Or i can download somewhere from Apple the "DMG" files ?

We in hard work now with our MS setup, and i afraid to loose our work.

Thanks for possible help, and sorry for nab questions. I'm new in OSX.