Here's how to determine which shank machine you have:
Put on your regular piecing foot and lower the foot. Using a tape measure, measure the distance from the bottom of the foot to the top of the screw hole that attaches the foot to your machine.
If the distance is 3/4" or less, you probably have a low shank machine.
If the distance is 1 1/4", chances are you have a high shank machine.