The filter on the left side of your projector (as you face the projector) can usually be pulled out after you open the door to get inside.
Cleaning out the projector filter regularly will lead to the best performance for your projector.
A couple of different methods could be employed, but the simplest method for staff would be to LIGHTLY knock the filter against the inside of a trash can, causing the dust to fall into the trash can. If weather allows, you may also want to LIGHTLY knock the filter against the outside wall of a building, releasing the dust from the filter into the air.
Eventually, your filter will get to the point that no amount of cleaning will help it and the filter will need to be replaced. If you suspect that your filter might be shot, let the IT Department know.