Usually when an electric dryer overheats it's because of a defective cycling thermostat or a clogged vent system. Clean any lint from the internal and external ductwork, and/or replace the cycling thermostat.
Although this isn't a common problem, one of the thermostats that controls the temperature in your dryer may break and cause the dryer to heat poorly. If so, you need to replace it. The thermostat is usually a small, round, black device mounted to an oblong steel plate. The plate is mounted to the internal ductwork . It will have 4 wires connected to it. 2 wires opposite each other will be closer than the other 2. The ones that are closer together should have continuity if it doesn't replace the thermostat.