Transmission fluid change

My sedona is reaching the point where transmission fluid needs to be changed (18 months or 36.000 km). I called a couple of dealers and got conflicting information. One says that not just the transmission but also differentials and something else need to be flushed. Another dealer says that Kia has no differentials and it's the transmission and something else (but not the differentials as Sedona doesn't have any). Does anyone know what exactly needs to be flushed?

Thanks.