Hi Joyce, you can start with the top ones and unscrew the separate cabinet boxes from the walls using a screwdriver. Be careful as when you loosen the last few screws the cabinet will want to fall off the wall. Best to have a second set of hands to help with this. You can then do the base cabinets in the same way. Instead of demolishing them completely there may be someone who would love to have them for their home or garage. Check with your neighbors, maybe they can make use of them.
Typically screwed into studs. Look for the screws and away you go. Best to have 2 or 3 people.
That’s fun but you could also remove them carefully and donate them to a Habitat ReStore or similar for reuse.
Are the cabinets in decent shape? Do you have a local architectural salvage store? If so, they might know someone who would come remove them for the purpose of reselling them, especially if they are antique.
If the cabinets really just need to be demolished, take the doors off first and then unscrew the cabinets from the walls as others suggest.