Best bet for changing the fluid in an automatic might be to buy a hand operated siphon pump and use it to "triple-change" the fluid when you do the filter and fluid change, because more than half the fluid stays in the torque converter even when you remove the pan. 

bulletRemove the pan, discard the fluid in the pan, clean the pan and change the filter. 
bulletRe-install the pan and fill to the proper level with new fluid.
bulletDrive the car for a few miles.
bulletUse a hand operated "siphon pump" to remove as much fluid as possible by way of the filler tube.
bulletFill with new fluid to proper level and drive the car a few miles
bulletRepeat siphon-drive-refill steps once or twice more.

That should come close to completely renewing the fluid.