For MANY firearms (but not all) the sights may be adjustable by the user. However, in the case of a shotgun with bead sights, or a revolver with fixed sights, they are not adjustable. Some semi=auto pistols have sights that can be adjusted by a gunsmith. Most rifles will have a user-adjustable sight.
Depends on the firearm.
You take it to a gunsmith
Best left to a trained gunsmith.
Best to ask a gunsmith for assistance
Best lef to a gunsmith
Your two best options are to find a gunsmith and find a gunsmith. By the time you buy the necessary book(s) you could have paid a gunsmith to do it.
You need a trained Browning gunsmith
Best left to a gunsmith
Best left to a trained gunsmith
Who made it? Your best bet is to find a competent gunsmith.
Best left to a qualified gunsmith.