Clean up duct:
Use the agitation brush to scour up the dust inside the dust. Collect this dust using your vacuum cleaner. The hose attachment of your vacuum is the most effective tool for it. Give close attention to the joints and corners because most of the dust accumulates there. Go as far as you can with the length of your vacuum cleaner. However, you might not be able to reach all the length of the duct. If you are using hose sections to increase the length, use a tape to secure them fully so that they do not come off inside the duct.
Open up the filter inside the duct. The filter helps prevent allergies from the dust and dirt inside. Replace the filter by getting the same model from hardware and home improvement shops.
After you are done with replacing the filter, attach back the grilles by using the screw drivers. Vacuum the exterior to clear up any dust remains
Clean up your vacuum cleaner bag periodically during the process to make room for all the dirt. After you are done, wipe the interior with a wet rag.