Mimo Momo
there will be a noisy sound (voooooooo) coming from your wheel while driving the car to test if it is remove your foot from the gas and you will find that this sound continues then you need to change them fastly or there will be some dangers on you (the wheel may jump from the car) hope i helped :D

Nomadd
You get the wheels off the ground and turn them by hand. If they're loose or feel rough when you turn them it's time for new bearings.

roger
you can either wash the grease off in a solvent tank and inspect the bearings for pits and discolered ends where the hardened material has worn off (also how much movement in the bearing race itself. Or do what I do on unknown mileage bearings toss them out and buy a good made in USA set. The made in china cheapo bearings are soft core with a hardened shell. And at some point they start to disintegrate and take out all the other bearings too. A good set of bearings are not that expensive and always buy a new grease seal

Mike
Does it make a wub, wub, wub sound when driving? Otherwise jack the wheel up and try rocking it up and down with your hand at 12 oclock and 6 oclock, have a buddy look on the other side when doing this to make sure the ball joints are not the ones moving. Rangers and Exploders are known for eating ball joints and tie rod ends so to diagnose correctly you need another set of eyes. If its a beater ebay is a good cheap sourse for a front end kit and wheel bearings. If its a keeper go with a set of Moog, expensive but will last till the truck is ready for the scrapyard.