Steps for replacing transmission fluid include loosening the bolts on the transmission pan, measuring the old fluid to determine how much new fluid is required, removing the used gasket, replacing the filter and adding the new fluid. The new fluid level should also be checked when the dipstick is hot.
All but one of the bolts of the transmission pan should be removed before gently taking off the last bolt, angling the pan away and draining the fluid into a catch pan. Old fluid can be measured by using a one-gallon milk jug. Once the old fluid has been drained, the transmission pan should be completely removed to change the transmission filter.
Once the used gasket has been removed, a solvent or parts cleaner can be used to flush debris from the pan and transmission. Care should be taken to replace the magnet inside of the pan once the cleaning has been completed. New transmission fluid can usually be added through a dipstick tube, but there are some vehicles that have a plugged hole where the new fluid can be injected. To ensure enough transmission fluid has been replaced, it's best to add the amount that was drained before driving the car for a while, shifting gears, and checking the transmission level again.