Hmm. A more common question is how one might *add* 4WD to a 2WD version (rather a more expensive and difficult proposition). Hmm.
I would suggest that although what you want to do is possible -- maybe even semi-easy if you will settle for a partial conversion (and depending on what year and options you've got) -- you'd be giving up a valuable capability, and ending up with a pallet of greasy heavy machinery in the yard, in order to gain very little. It'd still be a heavy, largish vehicle. A quick glance around fueleconomy.gov makes me think 4WD costs you about 1 (one) MPG both city and highway in this vehicle, given similar engine and tranny choices.
BTW, you didn't say what you mean to tow, but 4WD -- especially with "low range" for those really special occasions -- can be useful for, say, getting up a slimy boat ramp.
If you want an Explorer and concomitant towing capacity but really would feel silly tooling around with 4WD that you never used, look for a good example that was born 2WD, is my suggestion. And if you want this particular vehicle, don't fret too much about its having 4WD.
Cheers,
--Joe