IF the system is working correctly, just put the gearshift in Neutral.
Press hard on the brake, and turn the switch to 4H or 2WD.
The Ranger and most other 4WD's will shift on the fly (in Drive) to 4H (4-wheel High), but require the gearshift to be in Neutral in order to shift out of 4L (4-wheel Low).
back up a few feet
Take transfer case apart its stuck I'm doin it right now
Back wheel drive
If it shows in 2wd and your sure it's still in 4wd. Back up it sometimes kicks back into 2wd. If that does work check the shift linkages.
On a 4 wheel drive capable Ford Ranger , the transfer case is bolted to the back of the transmission and allows power to be transferred to the front wheels
Back wheel drive
behind driver side back seat under cover.
Front wheel drive.
You have to be stopped with the transmission in neutral when you shift in or out of low 4 wheel drive. Park doesn't work as neutral. When you push the rocker switch up for high 4 wheel drive once you will be in high 4 wheel drive, push it again for high 2 wheel drive, you can shift between high 2 and 4 wheel drive while you are driving.
All are either rear wheel drive or four wheel drive.
If you are in 4-HI, just give it more muscle pressing down on the lever. If you are in 4-LO, give it more muscle while the TRANSMISSION IS IN NEUTRAL and you are rolling at 2-3 miles per hour. If 4-wheel drive does not immediately disengage after depressing the lever all the way, stop the vehicle put it in reverse and back up several feet, put it back into drive and you should be good to go. If 4-wheel drive is stuck and the 4-wheel gear moving easily but will not go out of 4-wheel drive
Smaller and stiffer shocks/springs on the front, remove a leaf spring or 2 on the back and get stiffer shocks/leafs back there as well.