Originally posted by rhyzin

Raise up the car. Remove the drain plug and drain fluid. Replace drain plug. Either use a funnel with a long tube or a tranny fluid pump (much easier) and replace fluid in filler hole. Replace filler plug, lower the car and you're done.
I have mobil 1 syn in mine. It works fine. It's seemed quieter.

Originally posted by jason33hs

If you have an automatic transmission, this might be the route to go. The auto holds 7.7 quarts of Dextron fluid. Mitsu service manual states:

A/T FLUID REPLACEMENT M1231001000179
If you have an A/T fluid changer, use this changer to replace
the A/T fluid. If you do not have an A/T fluid changer, replace
the A/T fluid by the following procedure.
1. Disconnect the hose shown in the illustration which
connects the transaxle and the oil cooler (inside the
radiator). Place a container under the hose to collect the
discharge.
CAUTION
The engine should be stopped within one minute after it is
started. If all the A/T fluid has drained out before then, the
engine should be stopped at that point.
2. Start the engine and let the A/T fluid drain out.
(Running conditions: "N" range with engine idling)
Approximately 3.5 dm3 (3.7 quarts) of A/T fluid should
be removed.
3. Remove the drain plug from the bottom of the transaxle case
to drain the A/T fluid.
Approximately 2.0 dm3 (2.1 quarts) of A/T fluid should
be removed.
4. Install the drain plug with a new gasket, and tighten it to the
specified torque.
Tightening torque: 32 ± 2 N⋅m (24 ± 1 ft-lb)
CAUTION
Stop pouring if the full volume of A/T fluid can not be
added.
5. Add new A/T fluid (DIAMOND ATF SP III or equivalent)
through the oil filter tube.
Approximately 5.5 dm3 (5.8 quarts) of A/T fluid should
be added.
6. Repeat the procedure in Step 2. (to pump out the rest of the
contaminated A/T fluid)
7. Add new A/T fluid (DIAMOND ATF SP III or equivalent)
through the oil filter tube.
Approximately 3.5 dm3 (3.7 quarts) of A/T fluid should
be added.
NOTE: Check for contamination or a burnt odor. If the A/T
fluid is still contaminated or burnt, repeat Steps 6 and 7
before proceeding to Step 8.
8. Reconnect the hose which was disconnected in step 1
above, and firmly replace the dipstick.
9. Start the engine and run it at idle for one to two minutes.
10.Move the selector lever through all positions, and then move
it to the "N" position.
11.Check that the A/T fluid level is at the "COLD" mark on the
dipstick. If the level is less than this, add A/T fluid.
12.Drive the vehicle until the A/T fluid temperature rises to the
normal operating temperature [70 − 80°C (158 − 176°F)],
and then check the A/T fluid level again. The A/T fluid level
must be at the "HOT" mark.

Hope this helps.

Jason