Find your existing air conditioner filter. Check beside the heating and cooling units' ductwork for it. Most air filters are in your actual heating system or in the floor, wall or ceiling. It will typically be enclosed with a slotted door.
Take out the previous air filter in your heating and cooling system. Lift up the metal covering over the existing filter to access it. You might have to remove screws or unlock a mechanism holding the cover in place. Remove the filter and properly dispose of it, once you have completed the next step.
Get the accurate electrostatic air filter size. It is vital to acquire the right-sized filter. Look over the filter for the size needed. It will be marked similarly to this: 12x12x1, 10x20x1 or 10x14. If no filter were being used in the unit, measure the dimension of the area the filter would fit into. Write this information down.
Purchase your electrostatic air filter. If you are unable to locate a filter in your exact size, you could use one that is adjustable or even get a custom one made. You can obtain these filters at most places where you can get regular ones at. They are also available from many websites.
Install the electrostatic filter. After you take out the old filter, check the new one for an indicating arrow or other warning of the filter's airflow direction. Place the new filter in the unit and then close the covering.