Try turning shaders off. If you don't know your computer's specs, I assume it's a prebuilt desktop. If it's prebuilt, I assume it's using an integrated graphics card. If you're using an integrated graphics card, they can only barely handle shaders properly, and it'll probably run much better without that.
If you know you have a graphics card made by AMD/ATI or Nvidia, then definitely go try updating the drivers, from their official websites. To check if you have a graphics card from AMD/ATI or Nvidia, open the start menu, type in "dxdiag" without the quotes, hit enter, and go to the Display tab.