The trim usually self destructs when you try to pull it off, unless you can get behind it and squeeze the tabs in. For the fender trim, take the fender off and it's easy. For the rear quarter trim, take the interior rear side panels out and you can see them. I'm not sure if you can reach the inside of the trim on the doors, but if you pop the door panel off you should be able to at least see if you can reach them. The door trim also has one bolt on the inside of the door, on the rear edge. When my car was painted I bought all new ones so I just yanked all the trim off. The downside to yanking is that it can slightly bend the metal around the tab holes, but you can bang it straight with a hammer. It's behind the trim anyway.
The stock door caps have one bolt on the inside of the door, right on the rear edge, below the trim bolt. Then just pull the bottom outward, and they'll come off (they don't break!). The stock sideskirts have about 14 plastic screws all over them. Two are just in front of the rear tire and are hard to get to unless you take the wheel off.