The mature durian usually has cracks. It's much easier to open the cracks. Use a fruit knife to pry open slowly along the crack, and make a circle along the skin to break it off.
There are cracks in durian, you can also carefully lift the fruit handle, the tail side toward the ground, to the ground, the same can be very easy to open, but such open can not be kept for too long, to eat as soon as possible.
Not all durians have cracks. If there are no cracks, you can cut a part of the tail with a fruit knife. After cutting, you can see the lines on it. Insert the knife into the crossing point of the lines, and just cut along.