Cleaning the Air Filter
Filter prevents dust from accumulating on the optical elements inside the projector. Should the Filter become clogged with dust particles, it will reduce cooling fans’ effectiveness and may result in internal heat buildup and adversely affect the life of the projector. If a “Filter warning” icon appears on the screen, replace the Filter immediately. Replace the filter by following the steps below.
1. Turn off the projector, and unplug the AC power cord from the AC outlet.
2. First, clean up the dust on the projector and around the air vents.
3. Press ◄ leftwards on the filter cover to release the latch and open the filter cover.
4. Pull out the filter. When taking out the filter, put your fingers on the filter tab and then pull.
5. Put the new one back into the position and close the filter cover. Make sure that the filter is properly and fully inserted.
6. Connect the AC power cord to the projector and turn on the projector.
7. Reset the filter counter.

The attachment below also provides you with step by step directions.