how does increasing the height of a ramp affect how far a ball rolls down the ramp

Hmm. . . You can't modify the ball or the ramp. Those are two constraints that don't leave much room for improvement. Is changing the pitch angle of the ramp allowed? I suppose not. How about moving the ramp into a vacuum chamber? If you place the ramp and ball in a vacuum chamber and purge the air, you will eliminate -- or at least greatly reduce -- the friction due to air resistance. In a vacuum, the ball should roll down the ramp faster. How about blowing the ball down the ramp? Get behind the ball and, once it's rolling, blow hard! Better yet, get a hair blow-dryer and really give it a boost.

The material of the ramp, the volume of the ball, and the mass of the ball.

A ramp exerts no force, just gravity.

You can control a lot during this experiment. You can control the weight, size, and density of the ball and the angle of the ramp, to just name a few.