Down unweighting, is a hard thing to describe to ppl, but once you feel it, it feels natural. What works for me is thinking I am sucking the board up to my body. Picture being in a standing position, and you take one knee and raise it up to your chest as much as possible while keeping the other foot on the ground, that is sort of the feeling, but it happens with both feet at the same time. Almost as if you went from a standing position to a catchers position in baseball, but you are not lowering your body, you are pulling your legs up towards your upper body enough to take your body weight of the board. It allows you to take enough weight off the board that it makes edge transition much easier, but lets you retain a great deal of stability at the same time.