Finisher (bizhub C3851FS)
Open the Left Cover.
Pull the tab.
Pull out the staple cartridge.
Lift an empty staple case while holding its both edges, then pull out it from the staple cartridge.
Mount a new staple case in the staplecCartridge.
Insert the staple cartridge until it clicks.
Return the tab to the original position.
Close the Left Cover.