bearings and sensors

Need some help here. My 96 Ranger 2.3 4x2 4 cyl most likely needs the rear wheel bearrings replaced. Also, when going up to 50 mph, the O/D off light comes on, and shifting is horrible. I am wondering where the sensor is so it can be replaced, and where I may find online how to do the rear bearring replacement. Any suggestions would be greatly appreciated.