There should be no reason to change the fluid in this transmission unless you are operating under severe conditions: towing, rough and dusty roads, lots of short trips (delivery service).
If you have to add fluid, it is added through one of two plugs under the transmission. One is a drain plug, which is the LOWEST plug, and the other, next to it but on a higher level, is the overfill plug. You remove that one and add fluid until it seeps out, then you are all set.
Be very careful working under the car.