Sorry to see your PC was struggling to run the game.
If you access the game's video setting, there 2 quick fixes to up your FPS:
1) Lower the resoultion:
* this will make the biggest different to how smoothly the game runs. By default the game will try to run o nthe highest resolution your monitor supports, but taking this down will give you a huge performance boost. Most systems should hit high frame rates at 720p, but the game actually looks really cool at even lower resolutions.
2) Switch off ambient occlusion.
* this won't make as big a difference, but will get you some extra FPS!