Gameplay : how do you choose which expansion to use on a save?

I play with 10 EP’s and if I remember right four SP’s along with about 3/4 of the Store and of course the requisite CC that I need for my gameplay desires :p

But all that’s about to change because I ordered me a new laptop that can hopefully play all 11 EP’s on ultra settings and I can finally have pets in my game that wouldn’t scare small children :D