I know there is life after death but when someone has died is it right to say he is an angel in heaven?
No. Angels are an entirely separate order of creatures from human beings, created to be pure spirit. Human beings are created to be embodied creatures with spiritual souls. Although a human soul separates from the body at death, it does not become an angel but remains a disembodied human being until the resurrection of the dead at the end of time. At that point, disembodied human souls will receive back their glorified bodies.