how do you change front wheel bearings on 1998 camry (4 cylinder)

You need to remove the wheel, brake calipers, and the rotors. you need to also remove the steering knuckle that is bolted to 3 places (the strut, the lower tire arm, and the tierod.) Push out the hub and bearing and replace them with the new parts. Then do everything in reverse. You will also need some very specific tools to do this job. I would recommend taking it to a mechanic to have the job done properly.

what is the approx cost for changing the fron wheel bearing by auto mechanic.

Big hammer and a vice