First, remove the cartridge from the packaging. Hold the cartridge on the sides and rock it gently from side to side. This will loosen the toner inside of the cartridge. If you look on one side of the cartridge, there will be a piece of tape sticking out of it. Carefully break the plastic connector that is holding this to the unit. Slowly but firmly pull on this tape. It will come out of the cartridge. (Be careful when disposing of this tape - there will be toner on it.) Remove the old laser toner cartridge from the printer. Pay close attention to how you remove the old one. Insert the new cartridge in the same manner. Close the printer and test it.
These instructions (with diagrams) may also be found in the printer manual or in the box with the toner cartridge, and sometimes on the underside of the printer cover.