Replacing toner in Brother printers is an easy task that doesn’t need a complex procedure. All you need is a genuine and correct replacement toner cartridge for your exact printer model. You can match the label inside the front cover, not the TN number, to find the correct cartridge match.
Here are the steps involved in replacing a toner in a Brother printer:
Open the front cover facing you.
Release the drum and toner assembly, and they’ll come out as a single unit.
Place the assembly on a flat surface. Look for the colored lock lever and press it down to slide the empty toner cartridge out.
Keep the drum unit down carefully away from light.
Unpack the new toner cartridge and remove its protective seal.
Slide the unpacked cartridge into the drum unit until you hear a click sound.
Slide the green tab on the drum unit once, and return it to the home position, matching the arrow on the tab. It’s important to reset the corona wire cleaning tab.
Finally, re-insert the combined drum and toner assembly into the printer and close the front cover.
After replacing the toner, print a test page via the built-in print function accessible from the menu. It’ll show a full-page pattern. You’ll see a “toner low” warning when 5-10% toner is still left in the cartridge. It means you can print up to 50-150 pages, depending on the graphics level.
Source: Replace Toner in Brother Printer