The configuration file would either be in the main game folder or in the folder with the saved games.
It might have file extensions like .ini, .inf, or .conf.
If you're lucky, you could open the file with Notepad and it would have something obvious like "antialiasing=on" that you could change.
If you're not lucky, opening with Notepad would show gobblygook.
If you uninstall, make sure the game folder and save folder are gone, and reinstall, it might fix the problem.
Not all games have a configuration file. Sometimes configuration information is saved in the registry, which would mean you'd have to run a registry cleaner after uninstalling the game.