Here is a link to the manual hub swap for '93-'97 Rangers: TRS Magazine - Ford Ranger Manual Hub Swap
But this doesn't change the electric shift issues, if that is what you are having.
If you shift into 4WD, and dash lights change, and one or both of the front wheels give you a clicking noise then yes the automatic hubs are the issue.
If you shift into 4WD and lights on dash don't show 4WD then the issue is the electric shift motor, read here: Servicing A Transfer Case Shift Motor
The problem with the electric shift is usually lack of use, shifting to 4WD even sitting in the driveway cleans the motors brushes, the brushes are what conduct the electricity and get the motor moving, they tend to get stuck and lose contact with rotor so when you shift into 4WD motor doesn't get power so no shift.
Tapping on the motor will often free up the brushes so you get temporary use, key word being temporary.
Here is a list of transfer cases used with Ranger: Ford Ranger Transfer Cases
You can get manual shift transfer cases, shifter sticks up thru the floor near where manual trans shifter would be.