This is correct, just slacken the philips head screw to release pressure.

 

There was a Philips screw I could see, although it was hard to get a screw driver flush on it. It was holdng a small metal bracket...... is that what needs loosening? Then the lock will come out?

 

AFAIK, yes. Most lock mechanisms are held in place by a sort of forked piece of metal, slightly curved, which slides into a slot in the lock, holding it hard up against the inside of the panel.

Door locks don't have any screws, maybe the boot lock has one to keep it in place.