Are you playing the game on a Desktop PC or a Laptop?
If it's on PC, I suggest that you update your GPU.
If it's on Laptop, I don't really think that Laptops are made to play high specs games (Unless it's a gaming dedicated Laptop of course).
If you don't want/can't get a better GPU. I suggest that you set Texture, Shadows, etc to Low settings and low the resolution of the game as well (The quality will get a bit creepy but it won't be laggy at least).
Let me know if it helps!
PS: Back in time, the game didn't run well for me as I had a Nvidia GeForce GT 120 with 1GB dedicated Video RAM) but after upgrading to a GTX 550 TI GS (with 1GB DDR5 VRAM) the game runs smoothly at medium settings).