Push in and hold the button on the bottom of the frame.
Either tap the barrels or the butt on something soft and they should separate. Keep one hand on each piece.
I recommend tapping the barrels, rather than the stock, because of the way the stock is attached.
If they haven't been off in a while, they may be stuck pretty tight.
Not bad advice, but, there is a possible big horsefly in the yogurt-what Charlin?
For about a decade after the purchase of the Charlin company by Darne, in 1955, one could get regular production model Darnes that were marked Charlin-I am told they were available in R, P and V grades, but, will confess to only having seen photos of a pretty much standard R grade that was marked Charlin.
If you are looking at a full steel receiver gun, with no wood under the area the breech slides on, and a push button in front of the trigger guard, you have a typical Charlin. The advice above about tapping the barrels rearward, instead of hitting the toe of the stock forward is a very good idea, and will save the toe of the stock or an old dry buttplate from breaking.
It takes tools and skill to get the sliding breech block off a Charlin, so, don't try that. If, when the gun is cocked, and you open and close the breech you get a "clunk, clunk" sound, the gun has a broken flat spring on the opening lever, a simple fix, I've seen and repaired more than one over the years. The gun should open and close smoothly and nearly silently, if it hasn't been fired.
Good luck, take a camera with and show us some pictures.
Best,
Ted
