How often should you change your transmission fluid?

Check your owners manual, there will be a section under maintenance that will show  how many miles there should  in between fluid changes As an example ford recommends it be done every 30,000 miles for most normal use cars but always it varies by car model.

The important thing to remember is changing the filter when doing a transmission service because the transmissions filter collects all the debris from the normal ware and tear of everyday use and just like a vacuum cleaner bag in your home gets full, them  plugs up and the vacuum motor makes noise that sounds like its straining and there gets to be no more suction and that's what happens to your fluid pressure if the filter isn't changed it plugs up ant starves the transmission pump of oil and your transmissions clutches and bands burn up because there's not enough fluid pressure to hold the clutch packs.

Some ford vehicles also have a drain plug in the transmission's torque converter, on these models it's a snap to drain the rest of the fluid and this is important especially on fords  because when the fluid gets old it oxidises and the torque converter clutch glazes and when this happen it will slip and chatter upon apply of the torque converter clutch with light to medium throttle @ about 40mph to about 55 mph. If caught right away and all the transmission fluid is changed the chatter will stop and the transmission's life will be extended!