You might want to leave the bottom half of the shell on in case the yolk is still absorbing, and when the chick is ready it should be able to kick itself out.
Sometimes, though I've had chicks too weak to even do that. If the chick is left in the shell too long, it keeps growing and the legs...
Yes, you need to intervene. Get some very warm water in a cup, and dip a paper towel in the warm water. As you peel the shell away, moisten the membrane with the wet paper towel. Be careful to keep the wet paper towel away from the nostrils.