There may be a way within Steam. I don't know. This is the only game I've ever bought off steam.
Within Civ V itself, look at the startup screen where you pick "Single Player", "Mods", etc.. There is a number at the bottom center of the screen. It should now say 1.0.0.62 if you have the patch.
Edit: Got beat by the Moderators. Man they are good.