Prong collars--or "pinch collars," as they are sometimes called--are made with prongs that connect together and provide pressure points all around a dog's neck. According to Ann Marie Falk at the University of Illinois School of Veterinary Medicine (see References 1), "Choke and prong collars can be very effective training tools when used appropriately, and many professional dog trainers use them as part of their training plan." Of the many common mistakes dog owners make while using these collars, one is improper removal of the collar.
Hold the prongs of one link between your thumb and forefinger while using your other hand to grasp the collar next to the chosen link.
Squeeze the prongs together.
Pull the prongs out of the link. The collar is now unfastened, and you can remove it from the dog's neck.