If you have been squeezing back on the control wheel you will need nose up trim which means rotating the trim wheel back towards you. To level off from the climb, lower the nose back to the straight and level flight attitude. Having established straight and level flight by squeezing forward on the control wheel, allow the airspeed to increase prior to reducing power to the desired cruise setting. Once you have adjusted the power setting and the airspeed has stabilized you can once again relieve the pressure you are exerting on the control yoke by trimming. In this case you will probably need nose down trim which means rotating the trim wheel away from you.
Most descents involve a power reduction.
Anytime the power is going to be reduced to a setting below the green arc marked on the tachometer, you should apply carburetor heat by pulling out the carburetor heat knob. Next, reduce power to the desired rpm setting. If no control inputs are made to change pitch, the airplane will start to descend while maintaining approximately the same airpeed as prior to the power reduction. However, as you approach an airport for landing you will usually want to descend at a slower airspeed than that at which you were cruising. To achieve this you need to raise the nose slightly following the power reduction.