I haven't tested it yet but my plan was to do like Dop says but instead of Ajax check if local storage "Version Number" exist
If not you know its first time he plays the Game
Else >>> Check the version number saved on local storage against the version that is about to play if it's lower then Update the Game and save the new version back to the Key "Version Number" into local Storage.
Also when the update is available then remove the Button Play and show just the Button Update so there is no other option other than the Update, is like forcing it no choice.
I saw many Games doing it and that's the model I would love to follow.