Hello and welcome to just answer. You will first need to remove the dash and then discharge the refrigerant from the system, drain the cooling system, then remove the HVAC housing set it on a bench then open up the HVAC unit to replace the heater core. Are you up to a task like this? If so I can send you the procedure from the service manual. This is a very labor intensive job, and if you are not sure you want to take this on, then it is best to let a professional do this.
Ok, here is the procedure for you.
WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, Refer to PASSIVE RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.