To drain and fill the transmission fluid, a mechanic will first need to lift and support your vehicle off of the ground to access the transmission. The process is similar to an oil change, except that it is usually necessary to remove the transmission oil pan to drain out the old fluid. For most automatic transmissions, the mechanic will need to remove the bolts that secure the pan to the transmission and lower the pan from the vehicle.
With the pan removed and the fluid drained, the magnet designed to trap metal debris must be manually cleaned. It is often recommended that the transmission filter be replaced as well, since it must be accessed by removing the pan. Still, transmission filter replacement is not necessary with a drain and fill service. Either way, the pan is reinstalled with a fresh gasket, and the transmission is refilled with fluid from either the dipstick tube or an access hole on top of the transmission, requiring a special pressure pump and adapter (an increasing element of late-model vehicles).