Start by draining the coolant and disconnecting the battery before you start removing the heater core here are the directions on how to remove the heater in the diagrams below. Check out the diagrams (below). Please let us know if you need anything else to get the problem fixed.
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.