The energy level decreases in an exothermic reaction. This is because energy is given out to the surroundings.
The energy level increases in an endothermic reaction. This is because energy is taken in from the surroundings.
Look at the energy level diagrams below. Which reaction is more exothermic?
The reaction shown by the second diagram is more exothermic. There is a greater difference in energy between the reactants and products. The green arrow is longer.