If the airplane is rigged and balanced properly. It should find the ideal airspeed and flight level all by it self. When you give it up elevator you increase the angle of attack. That slows the airspeed and shortly reduces the lift. You should have the trim set for the best glide when approaching to land. With trainers they have so much drag that you can fly with the same trim all of the time. As you fly more capable airplanes you will not be able to fly with out changing trim from power flight to glide.