To check whether your front wheel hub bearings are operable, accelerate your vehicle to 40 - 60 km/h and then, turn the steering wheel left and right 20° maximum. If the humming increases as you turn the steering wheel to the right, it means the left wheel bearing is to be replaced; if the same is true for turning left, then the right bearing should be replaced.
The noise will grow louder even when cornering smootly; keep that in mind in case you're unable to test the method described above.
To check if your rear wheel bearings are operable, spin a respective wheel manually, and try to wobble it.
Jamming, jerking movements and free play point out that a respective wheel bearing has exceeded its life time. Detailed replacement instructions can be found in video tutorials on the Internet.