I can't change the graphics settings, resolution, and anti aliasing

[RugC]

Before i bought the game, i pirated it for free and changed the settings to lowest as possible. After some time, i deleted the pirated version of the game and bought it at steam, once i opened the game i noticed i can't change the resolution like my previous settings for my resolution is 1280 x 720 but on the display it looks like 1920 x 1080. same goes for my anti aliasing too, it was off before i bought the game but now on the settings, it says its off but on my screen it doesn't. How do i fix this?