The safe and idiotproof way to change the fluid is to drain it overnight into a drain pan or big plastic tub. Then measure the amount drained using a 99 cent plastic juice pitcher you can get at Walmart that has measurement markings on it. Next, go back to Walmart* and buy the number of quarts of Dexron III fluid you'll need to match the amount drained.
Next install the drain plug and pour an exact amount of new fluid into the transmission. Start engine, shift through all ranged engine in Park and check the transmission fluid level using the procedure outlined the the owners manual. Later in the day, double check fluid level when engine is fully warmed up.
[ March 12, 2003, 07:55 PM: Message edited by: Patman ]