Your first solution to this problem install new drivers for a video card. This action can drastically rise game FPS. Also, check the CPU and memory utilization in the Task Manager (opened by pressing CTRL + SHIFT + ESCAPE). If before starting the game you can see that some process consumes too many resources – turn off the program or simply remove this process from Task Manager.
Next, go to the graphics settings in the game. First – turn off anti-aliasing and try to lower the setting, responsible for post-processing. Many of them consume a lot of resources and switching them off will greatly enhance the performance, and not greatly affect the quality of the picture.