Transmission fluid and filter change help

Generally there are two methods. One is the draining from the pan on the tranny. It basically replaces the fluid in the tranny but there is usually still fluid in the lines to the radiator and radiator. The new will mix with the old. Then there is a flush where all fluid is pushed out of the system and it is generally cleaned. More expensive and should be performed at a garage with the proper equipment to complete the flush. The first you could do yourself.