Doesn't look like you got much help on this one, so I'll throw this out. My experience is all with my Z06, but this may help a little.
First, I think this is easy and I bet if you get under the car you'll find it is self explanatory. I can't remember any of the sizes of the plugs, but it might not be the same anyway.
Start by raising the car. I bought four Rhino Ramps at Walmart and a racing jack (Sears sells a good one for about $165 or so).
With the car up and level, look at the tranny. The drain plug should be on the bottom. For the Z06, the tranny fill plug is on the drivers side, halfway forward, and two-thirds the way to the top and clearly labeled "fill". The Z06 tranny temp probe plugs into the fill plug so this need to be unplugged, then the fill plug removed. I suggest not draining the tranny until you verify you can open the fill plug. On the Z06, the drain plug is passenger side rear on the bottom.
For the Z06 diff, the drain plug is on the bottom (13/16th socket comes to mind) and the fill plug is on the back (this is a big allen head plug). Again, suggest not draining until you get the fill plug open.
Once each is drained, replace the drain plug, then pump the appropriate fluid into the fill hole using something like this:
AMSOIL Hand Pump
The GTO tranny takes 4.6 quarts and the diff takes 1.7 quarts according to online databases.
AMSOIL products:
AMSOIL ATF
AMSOIL Severe Gear Extreme Pressure Synthetic 75w140
Linear Mode
