Open the stapler door.
Pull out the staple cartridge from the finisher.
Hold both sides of the empty staple case with your fingers, pull, and then lift the empty staple case from the cartridge.
Remove the spare staple case from its holder.
Insert the spare staple case into the staple cartridge.
Push the staple cartridge into the finisher until it clicks into place.
Replace the spare staple case for future use.
Close the stapler door.