Wheel Bearing

I have a 1990 lumina, bone stock except for heavy duty cooling and a/c. I can tell one of the wheel bearings is out by the moan when driving, and my decrease in gas mileage with the replacement of the o2 sensor (that fixed the rich smell.) How can I tell which one it is without paying the tire shop and how hard is it to replace (steps?)
THanks
Roger

welcome to AF

Jack up the car and check for freeplay at the wheel. Don't be suprised if both are bad. Other than a few special tools (axle nut socket, t-55 torx socket, torque wrench and possibly a hub puller) the job is no more technically difficult than doing a brake job.

Seems like on the older ones, if they'd been doing it for a long time, there was a groove worn in the hub so bad it had to be replaced also...(rear)