It can be very frustrating to struggle with a knot that just won't come undone. Fortunately, there are couple of techniques that make this processes much easier. Both techniques require the use of tools; however, most people will have these tools lying around their homes. The difficulty of these techniques will depend on the type of rope you're working with. Nylon rope, for example, is slick, making it much easier to remove a knot from.
Secure one end of the rope in a clamp as close to the knot as possible, leaving the other end of the rope and the knot unclamped. If you don't have a clamp, ask a friend to hold the rope securely.
Hold the loose end of the rope and grasp it firmly with a pair of needle-nose pliers.
Hold the pliers by the handles push the nose of the pliers through the knot to force the end of the rope through. Depending on how tight the knot is, this could take a few tries.
Remove the pliers from the rope end and pull on the rope until the knot comes undone or is loosened enough for you to undo it with your fingers.
Hold the knot from the base.
Push a flat screwdriver through the centre of the knot.
Wiggle the screwdriver around until you feel the rope loosening.
Remove the screwdriver and pull on the knot. If it does not come out, repeat the steps above.