I thought I'd post this info since the transfer case fluid change is a hot topic as of late.
1. Do NOT put the car on wheel ramps! You want it as level as possible. You could preferrably jack up the front a couple of inches (secured with jack stands) so you can scoot under it. If you have access to a rack, that would be even better.
2. Remove the TOP fill plug FIRST by using a 3/8" ratchet extension end (fits right in the plug). It'll be tough because some kind of sealant was used to secure the plug.
You remove the top plug first in case the drain plug removes easily and the top plug cannot be removed. I wouldn't want you to drain your fluid and then be unable to remove the top plug to refill it.
3. Remove bottom plug and drain fluid (note: Dexron III transmission fluid is RED and what you're draining out will probably be black!). You may find metal shavings in the fluid. Whether this is normal or not is up in the air, but don't sweat it for now unless it's 'silver glop' instead of fluid you drain out! Replace drain plug.
4. To refill, use DEXRON III automatic transmission fluid, preferrably a reliable brand such as Valvoline High Mileage or Texaco. You will need some kind of bottle that will have a spout that will fit up to the top plug for refilling. I went to the Beauty salon supply store and bought an angled spout bottle that I could fill up with fluid and then empty into the hole. You could also use a sports drink bottle with an angled nipple.
5. Fill until it runs out the top hole. When this happens, you'll have about 1.8 qts. of fluid in the case. Replace top plug.
6. Drive you car for about 3000 miles and change it again!
It took 3 changes to eliminate my clicking noise. It is possible that this won't correct the problem on some vehicles and your transfer case may need replacing (forbid that to be the case!). I wish you well.
Here is a pic of the transfer case, courtesy of Wolfgang's ML page:
Wolfgang's ML Page