evaporator coil

hey there just found out my evaporator coil is all plugged up with black crap and looks to be leaking oil??? i took the heater core out and cant seem to get the evaporator coil out or even where to start to get it out the air conditioner on the car is dead so im not worried if i screw it up can someone help me out here because its blocking the air flow for the heat and i hardly get any heat the car is a 90 olds cutlass supreme international 3.1

See instructions on autozone.com/repairinfo