Here's some recommendations, with photos:
Pic of the recommended tooling you'll need. The drain/refill plugs in your '98, if original OEM, are internal wrenching 10 MM hex plugs. I show a 10 MM hex bit with a 1/2" breaker bar to remove the plugs. If the plugs have never been removed be prepared for a struggle. You may have to use an impact wrench to get them out. The pump showm is great for pumping the fluid into the TC. It is available at Advance and O'reilly Auto Parts. I use a 19 MM box end wrench to install the new plugs. Shown is Valvoline Max Life DEX MERC ATF (which I use in my AW4) but I normally just use Advance Auto Parts DEXIII/MERC ATF in my NV242. You'll need three pints of ATF (two quarts).
I recommend replacing the 10 MM hex plugs with flanged external hex plugs. These are 19 MM Wrench head plugs from NAPA. I use the 19 MM wrench to install them. The part number of the plugs are in this pic:
Like has been said, remove the FILL plug first, then the drain plug. If you remove the drain plug first and drain all the fluid and then can't get the FILL plug out you will have fun trying to refill the TC. I have heard of refilling it through the vent hose fitting...not fun.
When you drain the TC examine the drained fluid. Check for metal suspended in the fluid (indicates advanced wear inside the TC). Also check the color of the fluid; milky fluid means the previous owner never changed the fluid (and probably doesn't wipe his arse either). If any of these conditions exist, I recommend filling the TC and driving your Jeep around for a bit then drain and refill it. Check the drained fluid again. If it doesn't look clear, do it again. I know, all this ATF gets expensive but clean ATF in your TC is the heart of its longivity.