What Marian said is correct. If there is an updated patch and you have the game set in Galaxy to receive all updated patches, they will download them automatically.
I did some looking and found that in order to get to Expedition mode, you have to start a new game. You can't get to it "in-game." This quote is from the GOG website which says Expeditions is included and that the GOG version is sold with the 3.0 patch,.. It appears there was a 3.1 update a couple of weeks ago, so make sure you have you game set for automatic updates in Galaxy.
Play with all major updates since launch: Foundation, Pathfinder, Atlas Rises, NEXT, The Abyss, Visions, the 2.0 BEYOND update, Synthesis, Living Ship, Exo Mech, Desolation and the 3.0 update, ORIGINS, Next Generation, Companions and Expeditions.