There are two ways to remove the lower door stainless moldings:
1. Remove the inner door trim panels, look in the door opening and you'll see small tabs bent over holes in the outer skin. Bend the tabs enough and the trim will come off with the mounting brackets. Install is the reverse of the above.
2. If you don't mind scratching the exterior paint, (perhaps you're going to restore the car and that's why the trim is coming off), you can pry the trim off from the outside. Use a wide, very stiff putty knife and pry outward. The trim will either pop off the brackets holding it in place, or the aforementioned tabs will bend and everything will come off.
Method #1 is recommended because bending the stainless can happen if you try to remove from the outside.
New retainer brackets are available from the club's manufacturing fund.