Changing the transaxle (transmission) fluid on an MR2 turbo is actually very simple. The only difficult part is removing the drain and fill plugs which can be somewhat stubborn, particularly if they have never been removed before. Click pictures to enlarge.
Which fluid?
I have tried Mobil One, Redline MTL, and Redline MT-90, and have the
best results with MT-90. The difference, in my case, was much easier
shifting, no more grinding on 3rd gear up-shifts, and easier downshifts
into 1st gear. I would have to say that the improvement in shifter
feel was significant when using MT-90.
Draining
The first step is to remove the fill plug. While this may sound
strange, it is best to make sure it can be removed before draining the
transaxle of fluid. I find it easiest to jack up the car and remove
the driver's side rear tire. This makes access to the plugs much
easier.
Tools used - 24mm socket.
Filler Plug:
Now remove the drain plug.
Another
view: 
Make sure the car is level. If you have removed a wheel to gain
access to the filler and drain plugs, just adjust the jack so that the
car is level. Fluid draining:
Once the fluid is drained, replace the drain plug. To fill the transaxle, I use a funnel, a tube (from Home Depot) and some duck tape.
Run the tube through the engine compartment and down into the filler
plug. Then place some sort of oil pan / bucket under the filler
plug to collect any excess transaxle fluid. You want to fill the
transaxle until fluid starts to run out of the fill plug. Make
sure the car is level when filling - it usually takes 4 quarts, sometimes
a touch more.
Tube inserted into fill plug:
Then just start adding fluid to the funnel. If it is particularly
cold when performing the fluid change, it can help to warm up the gear
oil by bringing it inside, or even putting it in an oven at very low
heat. Wives love it when you do that! This will help it pour
and drain into the filler more quickly. It does take time.
Allow any excess fluid to drain from the filler plug, replace the filler plug, and your done! I usually replace the fluid once per year, and have been using Redline MT-90 for about 6 years now.
