How much ATF Fluid does the Envoy Transmission take?

I would like to change the Transmission filter and fluid my self but am not sure how much ATF Fluid does the Envoy transmission take. I have been using Mobil 1 products ever sience i have bought my vihecle back in October 2002 and 53,000 Miles later, runs like a charm. Because almost all other shops just do the "flush" service and no filter change, what would be the purpose of the filter if you dont service it, and replace it. Anyways, does anyone know how many quarts would i need for the change? Any help is greatly appriciated.