I'm not familiar with these brakes, but you should be able to turn the nut between the conical nut at the top and the brake arm - that will lower or raise the conical nut. See how the thread has flats on it where it protrudes? That locks in to the rectangle hole in the brake arm so it doesn't turn when you make the adjustment. Does that make sense?

Edit: everyone jumped in while I was making a coffee.