In that case there shouldn't be anything for you to do. Assuming you have an active internet connection and you are not starting Steam in offline mode, the game should update automatically.
You can also verify the version number of the game (it is listed on the lower right side of the main menu screen). As of right now, the latest version is 4.1.1.3911062
Thanks so much, Bomor--that's exactly what happened! And thanks to everybody else for all the help.
