Well, before you ask that question :P Update your video cards drivers and get the latest everything for your computer. Otherwise, you may have to look at upgrading.
At the time being, there is no way to reduce the graphics for Toribash and I doubt there will ever be a pirority to do it. There has been plenty of people with the same problem as yours and they seem to have gotten it fixed by updating the software. Have a look around the support forum and you may find other peoples ideas.