Help with heater core removal AC truck

[conoco]

Some say you can remove the heater core from inside the cab and then some say you have to do it from under the hood. I already have my inner fender and everything off because I'm doing other work. But I can't see how to get to the heater core either way. Can anyone guide me on how to do this. Thank you.

Attached pictures are the box in the inside and the one under the hood. Thanks.