Here is how to replace an air conditioner filter in a home air-conditioning unit. This is a very easy do it yourself job. First, locate the air filter in the air conditioning cabinet, and make a note of which way the airflow arrow points, and the size of the filter. Buy a new air conditioner filter at any home-improvement store and remove the old filter and replace it with the new filter, making sure that the new air conditioner air filter is right side up, and that it fits properly in your home air conditioning unit. Changing the air conditioner filter regularly keeps your air conditioning unit clean inside, making it last longer, and a clean filter allows more air to flow than a dirty filter does, so it is a good idea to replace your air filer regularly.