Replace the automatic transmission fluid lines by jacking up the vehicle, draining the transmission fluid, removing the lines from the transmission and the radiator, and replacing them with new lines. The vehicle must be jacked up and secured on jack stands, both front and back, before crawling under the vehicle.
Drain the transmission fluid by removing the plug in the bottom of the pan on the transmission. Have a container ready to catch the fluid. Some transmissions do not have a plug in the pan. These models require removing the pan by loosening the bolts holding it on, and gently prying the seal loose to allow the fluid to drain.
Trace the transmission lines from the bottom of the radiator to the point where they connect to the transmission. Make a note of the path they take so the new lines can be routed n the same manner. Disconnect the lines from the transmission using a flare wrench, and remove them from the radiator. The radiator connections may be accessible from underneath the vehicle or underneath the hood in the engine compartment.
Slide the lines away from the vehicle. Do this from the transmission end of the lines and not the radiator end. Install the new lines, and refill the transmission fluid.