Power off and unplug the unit.
Remove the metal air filter plates. Refer to the manufacturer's documentation for the unit for the specific filter removal process. The removal mechanism for this filter is usually marked clearly on the unit.
Rinse the filter plates under warm water. The debris will come off easily in most circumstances. A light wipe with a paper towel or sponge will remove any remaining debris. Some models may require simply wiping with a damp cloth.
Dry the plates thoroughly. Use a lint-free cloth for this step or simply allow the filter plates to air dry for several hours.
Reinstall the filter into the unit.
Your unit may also require that the internal ionizing wires be cleaned. A cleaning mechanism is usually provided with the unit that can be slid up and down on the wires to clean off the particles and then be placed back into its holder. This should be done every two weeks or as recommended by the manufacturer.
Plug the unit back in and turn it on to continue use.