Remove the weatherstripping across the cowl, remove passenger wiper arm, remove Black trim at base of windshield, remove blower motor, resistor, and hi blow relay. Remove the screen at the base of the winshield and then remove the heater box, careful not to crack it, there is a screw tucked in there by the fender that is hard to see. Remove the ground strap on the heater core (if its gone or corroded in 2, then get a new one. it helps keep from core corroding). Remove heater core and heater hoses. Install is reverse of removal. HTH
Be sure when u refill it to get all the air out of the system and clean the drain hole out at the bottom of the A/C box. And be sure to use a sealer when u put the lid back on, Black Silicone will work, but 3M makes a sealer just for this.
I know this prob isn't specific enough, but I don't know the exact number of screws in each location. I believe 3 hold the screen in and about 12 for the top plate of A/C box. Be careful not to bend that Black trim piece or your wipers won't park at the stops like they r supposed to because the blade will get caught.