In regards to the front:
Check out my post where I replaced the steering knuckle. The ABS sensor is located in that hole on the right side of the broad shiny area of the knuckle in my first picture (toward the front of the car, on both sides). If you take a look on the back of the knuckle, it's the only thing that has a wire running to it, and is secured with a single 10mm-ish size bolt.
steering-knuckle-replacement-guide-t593813.html
Ideally you'd be able to undo the bolt and simply pull it out to replace it, but the unanimous experience here is that they're always rusted and fused into the knuckle, and you'll need to remove the wheel hub and hammer it out from the outside.
I don't know precisely where they are on the rear or how to remove them, but it should be a similar setup, and again will be the only wire running to the back of the wheel. It's probably safe to assume those will be fused in place too.