Open the front cover of your Brother printer to expose your toner and drum unit assembly.
Pull out the assembly.
Unbox your new drum unit.
Looking at your toner and drum unit assembly, push down the green lever to release the toner cartridge from the old drum unit and install it into your new drum unit.
Discard old drum unit properly.
Slide the toner and drum unit assembly back into the printer.
Close the front cover.
Regards,
Jimmy