To update you will need to close the game down and re-launch for it to update. If this does not work for you or you feel it has not updated you will need to restart Steam.
Even if that doesn't do the trick, then verify the game cache will.
Released: 9 March 2015
As always the update is save game compatible.
Upon update your game version number will be: 15.3.1 PC: 615248; Mac: 615253; Linux: 615255
If you have any issues following the update, or if you think you've spotted a bug, please report it on the official Sports Interactive Bugs Forum.