I have a '47 Mercury convertible and need to replace the upper spring on both door latches. I am not sure the best way to remove the broken one and install the new one. It is held in place on one end by crimped metal tabs.
I did the same job on my '46 Station Wagon. The small metal tabs can be bent open enough to allow the spring to be removed and a new spring installed. I used an old screwdriver sharpened to a sharp chisel point and worked my way up to a thicker screwdriver. Once the new spring is in place you can use a vise grips or pliers to close them. You might need a couple of needle nose pliers to install the spring.
Post #2 is pretty much spot on. I will add though, he got lucky bending those tabs straight and then back over without breaking them.
I have done this task more times than I'm able to recall. I strongly suggest you get the little tab(s) red hot, bend it (them) as needed. Replace the springs red hot, bend them back over.
Follow Kube's advice as most of the time those little tabs will break when bent. Even if you are lucky enough that they don't visibly break when reinstalling the spring, they will most likely develop a hairline fracture crack that you can't see and break off later on.
As I recall, on my 40, I either silver soldered or brazed rebent tabs in place. That was 40 years ago. No problems yet.
I always anneal the parts you need to bend to replace springs in latches and winders. I use the smallest Oxy/act tip I have and keep the heat on the part you need to bend as short as possible. Like Kube said, just red is enough. Bending any metal back and forth work hardens it and that is why it breaks. Annealed metal will bend within reason without cracking.
C&G has the latch parts you need. (800-266-0470) They have both springs for your latch
11A702267, lower, and 11A702267-A, upper. You should also order the spring clips B702269, as well. Door latches take a real beating in older cars, and are a real challenge to repair because some of the tabs are prone to breakage when bent and repositioned.