Just for the record this revolver has 6 springs, which "the spring" are you asking about?
I assume you mean the main or hammer spring? First, there is really no reason to replace this spring just because of the age of the revolver unless, maybe, it has been cut to lighten the trigger pull.
If you do replace it use a S&W factory spring. There are after-market springs available but there is no reason to use them, they are NOT better than factory springs.
Now, first remove the sideplate. To remove the hammer spring cock the gun and you will see a small hole in the hammer strut. Place a piece of wire in the hole, hold the hammer and pull the trigger. Let the hammer down until the load on the spring seat is on the wire, then push the hammer forward. The strut and now captive spring can simply be lifted out.
Once out of the gun you have to disassemble the strut. Using a vise preferably set the jaws just far enough apart to let the strut pass between them freely. Push straight down on the strut to compress the spring enough to take the pressure off the wire and remove it. Release the spring carefully. From here it is the customary "Re-install in reverse order."