I used "oops" adhesive remover as recommended in another thread; no other tools were required. I'm not even 100% convinced that the remover was required, but I'm not taking them off again
1) squirt Oops around the reflector, front & back
2) push reflector into the wheel well, starting at the front top or bottom corner
3) work around the perimeter of the reflector pushing free from fender
4) "roll" off remaining adhesive with a finger (like Picus said)
Be careful on the rearward edge of the reflector -- there's not much plastic holding that fender edge on!