Most of your ATF resides in the torque converter - it is a fluid coupling. You drain it from the drain plug, and can refill from there too, but obviously check level again after everything is all back together, and don't let the engine run for long at all until level is back to where it should be.
The fluid you want is Dexron III. I don't know if you'll get much benefit from the synthetic - just change it as sepcified (every 30k or so if I remember right).

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