Both my Ford and Ram use a floor mounted transfer case shifter but his should be the same if you use a knob. Switching between 4wd high and 2wd can be done while in drive under motion if the drive train is not under load and you are traveling in a straight line. Switching in and out 4wd low is always done in neutral or park at full stop. Driving slightly forward or back to rock the truck in place and sawing the steering left and right may be needed if the drive train is bound up, but it's best to avoid binding up the gears rather than trying to correct for it after the fact.
