First disconnect the power to the unit. You will need to do this repair from under the bottom of the dishwasher. Remove the toe panel and look where the ends of the heater comes out of the tub. There will be a wire on each end. Unplug the wires. Next you will see a big plastic nut on each end of the heater. Remove the nut from the heater. There will be a washer on top and bottom of the heater. Lift the ends of the heater out of the tub and slide the heater out of the brackets. Reinstall is the reverse of the above. Here is a link to the parts diagram to help you.
Heater parts replacement parts for WHIRLPOOL KUDM01TJBL1 UNDERCOUNTER DISHWASHER | AppliancePartsPros.com