Without going through a long description of how they build these things,
There is a very strong likelihood that the cabinets are screwed in from the outside, both down from the roof and through the front and sides before the outside finish was put on.
Big challenge to remove them without taking a lot of stuff apart.
But in answer to your question, you can likely take the bottom of the cabinet out from the inside. It is most likely stapled on to the framing of the cabinet itself.
As for the other fastening points, you could carefully drive a skinny wedge in between the cabinet and the ceiling and walls, then insert a hacksaw blade to cut the screws. Be sure to get a thin piece of aluminum flashing or similar to lay against the ceiling and wall panels so you don't damage them.
I have done this, it's a pain to do and requires patience and time.