Peel back the organiser section in the lid by about 5 inches. Don't worry about the stitching
as it is dummy stitched.
Peel back the leather that covers the underside of the hasp you wish to replace. Once again don't worry about the stitching.
You should by now have revealed the back of the rivets that hold the hasp onto the case. Two types of rivet are commonly used. The first type has two legs that can be straightened with a flat headed screwdriver and extracted. The second usually has a washer capping it on the inside which can be carefully drilled out with a cordless drill.
Put the new hasp on, tapping down the new rivets with a hammer and reverse the process gluing the lining as you go (Evo-stick is best).