Not sure of your experience level, but if these are your first flights, congratulations on not totalling the plane.

Most beginners experience "pitching" of the plane because they don't have a feel for the plane. They may be accidentally putting pressure on the elevator when applying ailerons. Coming out of turns this is particularly evident for a couple reasons. First, they tend to let the nose drop during the turn. This causes a slight dive, and an increase in air speed. Since the trainer is designed to climb with speed, when you come out of the turn faster than you entered, the plane will climb. Secondly, holding the elevator after trying to level the wings is also very common, which results in the same behavior.

I can't count the number of times students have said to me "I don't know why its trying to climb". I tell them level the plane and then release the sticks completely. They're always amazed that the plane continues flying straight and level with no input.

Now if your plane "just jumps" with no input, that could be either turbulence (what were the weather conditions) or a bad receiver or transmitter. If they're new, send them back to be checked out. If they're used, send them back to be checked out, even if it costs a few dollars.

Finally, and most obviously, get somebody with experience to fly the plane for you and see what they say. There are a host of other mechanical or electrical problems you could be experiencing. Nicked servo wires, stripped servo gears, wing incidence, stabilizer incidence, and so on.

Brad