I see that others have already given stern warnings. I am not trying to ruin your day or to be rude, but I will add my advice.

First, if you have to ask, you are not qualified to do a proper action job, which involves smoothing more than lightening. That out of the way, here is what you need to know, direct from a reputable manual on do-it-yourself gunsmithing of the S&W revolver:

"To bend mainspring to obtain lighter, reliable trigger pull weight:

Step 1: Remove and keep all parts of your revolver stock, and modify only replacement parts. You will need all of your original parts later. See step 4.
Step 2: Buy several replacement mainsprings.
Step 3: Prepare yourself for how unhappy you will be when you turn a perfectly reliable revolver into a piece of junk that will not reliably fire a cartridge.
Step 4: Use all of the original parts saved from Step 1 to restore your revolver to stock condition, and hope it works after your "kitchen table gunsmith job."