I need help with the system settings for games on my pc?

I have a nivdia 8400 GS so I p the recommended requirements for most games but not all I am playing a kane and lynch demo and it has this lag to it that i cant fix I downgraded the resolution and theres some settings that I dont know what they mean but i was just wondering if besides downgrading my resolution is there another setting or 2 to downgrade to increase performance