Shut off the air compressor, and remove the air from the tank by opening its relief valve with a pair of pliers.
Close the relief valve, and loosen the screw clamp on the end of the pneumatic hose with a screwdriver, by turning the screw counterclockwise.
Remove the pneumatic fitting from the hose, and discard the part. Place the neck of the new pneumatic fitting in the hose, and slide the screw clamp over the neck.
Tighten the screw clamp over the neck of the new fitting with a screwdriver, to secure the fitting to the pneumatic hose.