Very easy to refill cartridges. I've done. Follow the following steps. First open the screws on the side of the cartridge that looks the iron plate, on the other side there is only plastic gears. Then open the top of the drum (green), there are filter of toner waste. On the side there is a plastic lid, open the lid, that is where the toner fill, fill to taste. Do not forget to clean the waste toner filter with a brush, careful to keep the green drum is not scratched. Then reinstall the side cover and put screws in all the parts that had been opened. Good luck.