To remove the barrel you will have to unscrew and remove the tang screw and the rear lock screw that enters the stock from the left side and holds the lock in place.
When you are removing the rear lockscrew, first, back it out about 2 turns.
Loosen the front lockscrew about 2 turns if one exists but you don't have to remove it from the lock.
With the lockscrews loosened, use a plastic or wooden mallet to lightly tap the heads of the screw(s) to loosen the lock.
I can't tell is the barrel is held on by wedges or pins but your question indicates that pins are used.
If this is true you will need a piece of steel that is slightly smaller than the pins.
Although there is no fixed 'rule', remove these pins from the left side of the stock, driving them out the right side of the stock.
Remove the ramrod and place the hammer at full cock and the barrel should lift out without difficulty. If it resists, do not force it. Look for something that may be holding it in place. The first thing to look for is to make sure the rear lock screw is removed from the gun.