When baking frozen pizza, why do the edges burn but cheese in center is not fully melted.
Frozen pizza tends to be baked directly on the rack. Also, toppings are probably a little more heavily dispersed toward the center. The edges have less protection from the toppings. Your edges cook more quickly because they are less protected by toppings. You can reduce your oven temperature to reduce the overcooking. If you really want to be meticulous about it you could place a large sheet of foil on your oven rack, then the pizza, then curl the foil over the edges of your pizza to offer protection from the heat.
The company that makes the pizza spend quite a bit of money on food scientists, therefore I suggest following the instructions exactly. However, if that doesn't yield good results, you can try to defrost the pizza on top of an oiled baking container (e.g. big metal pan), and bake on it instead of directly on the rack. It could be that while the edge of the pizza are cooking, the centre parts are still melting.