This is going to show my nerdiness, but judging from the default application icon for the game demo, I'm assuming you're using GameMaker? If so, it handily includes a function which tells you exactly what OS the game is running on.
Otherwise, I'm gonna have to go with a generic suggestion and say the Windows SDK does include a way to detect what OS version the game is being run under, which works as far back as Windows XP and as current as Windows 10 and beyond (at least according to the most current documentation I can find).
Hope that helps!