How do I remove pieces of my porch ceiling/soffit? (aluminum?)
Yeah, they're nailed on hidden flanges. You'll want to disassemble one end (wherever it's easiest to remove the fascia and/or trim channel) and pull nails one at a time. Be sure to keep track of order because they may vary in length somewhat.

Attempting to remove one panel in the middle of the run is almost guaranteed to result in damage.