Normally, there is a launcher that gives you the option to change video settings. If you aren't getting the launcher be default, go to the Batman2 folder, and you'll see a "RunLauncher.bat" program. Run that and it'll bring up the launch program with an Options menu that lets you configure the game to your liking.
If you have it downloaded from Steam, you should be able to find it here:
C:\Program Files (x86)\Steam\steamapps\common\Batman2