You've never used custom sounds before?
If you don't already have custom sounds that you want to save, just delete your sounds folder and put the Sketchwork's in its place.
What I do is pick a plane I want to focus on and then listen to all the engine/flaps/gear/gun sounds from every sound pack and put the ones I like into that plane's sound folder. Just look at one of the sound packs to find the right folder names for the right planes. The sounds outside any plane/vehicle folder apply universally unless the plane you're in overrides them with its own sounds. Example: you want to make all 50cal guns use file A except plane B, which you want to use file C. File A goes right into the sounds folder, C goes into sounds/plane B.
Hope that explains it well.