Make sure you give a big crest release to start with
You should never learn to crest release by just giving a big crest release. I've seen so many riders that have learned to just throw their hands up the neck, and then after the jumps they are totally unorganized and they have a horse/pony that runs away with them. You don't want do just put your hands up on the neck, a proper release is your hands following your horses mouth while he jumps.
Before even thinking about doing a proper release the rider needs to be balenced over the jumps. A good way to learn this is by tying a knot around 1/3(below 2'7) to 1/2(round 2'7 or higher). Holding one hand out in the air and the other on the knot and do a grid( with bounces, one strides, etc). The idea is to eventually progress to no hands, then no stirrups one hand, and then to no hands no stirrups. When the rider is balenced over a jump, the release comes pretty naturally