Turn off and unplug the air purifier.
Place your fingers in the recesses on the sides of the top of the front grill. Pull firmly to remove the grill.
Pull the old filter straight out to remove it from the unit. Take notice of the direction of the flaps on the filter that form the seal.
Press the new filter firmly into the air purifier. Position the filter so the flaps are in the same position as on the old filter.
Line up the tabs on the bottom of the grill with the openings on the air purifier. Push the top of the grill forward until it snaps into place.