Heater Core Leak

I have a 93 GMC Safari. It has had a very small coolant leak for a while. Yesterday I changed the passager headlight and was finally able to see the leak was coming from the bottom of the heater core on the fire wall on the passagers side of the engine.

Thus my question.

How do I remove the heater core to find out what is actually leaking?
As much detail as possible please. Do I have to go in through the engine compartment or inside the cab. I am not a mechanic but am willing to give it a go.

The fan in the heater core also makes some noise occationally when the fan is on high.

Thanks for all the details in advance.

David