Disconnect upper transmission cooling hose (careful about the o-ring inside). You may need a $15 tool that opens the c-clip (right terminology?)

Connect a clear plastic pipe with 3/8 inner diameter (ID) (Hardware store) to it and put the end inside a collection pan.

Start car and collect two quarts or less, definitely right at the bubble (very important!) start to appear on the fluid flow, otherwise air going into the system will damage your transmission. If I were you I collect about 2 quart and shut the car off before the bubble appears.

Turn car off.

Repeat this process until fluid is clear and shiny.

Upper cooling hose is the easiest way to change fluid. However, the fluid in the radiator cannot be accessed. To get that fluid circulating, I suggest, after replacing and adding the 1st batch of fluid, re-connect the cooling hose back to the radiator and run the car. Next, remove the 2nd batch of fluid and so on and so forth. I reconnected the hose without the clamp and it did not pop out of the radiator while the car ran for a minute.

Transmission fluid change interval
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I saw a significant fluid discoloration after 12k miles. I recommend changing fluid earlier than recommended interval and see the nature of transmission wear and tear, thus adjusting fluid change interval suiting your transmission.

Ronjon
'93 850