Your trainer will most probably fly best with some downthrust, maybe as much as 3 degrees. As to your original question, would changing the ailerons to have both slightly up help; most probably and worth a first try for an easy fix. More probably you have to little angle of attack on the wing or possible to much angle of attack on the stabolator. If so change the one which is easiest to change, usually by shimming the wing as the stab is most probably glued in place. As to downthrust, trim out the airplane so it is flying level with half throttle. Now apply full throttle, if it tends to tuck under, you have to much downthrust, if it thends to balloon up, you do not have enough downthrust. It should just increase in speed with no dive or climb as you increase the throttle if the thrust line is correct.