To replace the thermistor (thermostat) in this model of dryer, you will need to
unplug the dryer
and remove the bottom front service panel (see first image below). The thermistor will be on the blower housing (Key 42 in the second image). It has a red/white and a black wire attached to it. Pull the wires off of the thermistor and replace the part. Reverse the process for reassembly.
The part number for the thermistor on this model is 8577274. You can order this part from the Sears PartsDirect website