You can cut out the dead top of the tree now or wait until spring. Just be careful not to cut into the green or living part of the tree. So sorry your tree suffered in the heat but looks like it is going to make it as it has lots of new growth. Just expect a different shape as you remove the top or leader of the tree. Removing the top growth will encourage side branching and your tree will most likely become more shrub like in shape. Keep growing, Marianne Binetti