I keep a 10 inch length of PVC pipe down near the pump, when the lid ring sticks, I tap it gently around the perimeter while using the other hand to unscrew it or at least create torque in the unscrew direction, 3-5 taps and it's off.
If the clear lid under the ring is stuck, look around the edge carefully, there will be about 4 little slits on the underside, you can put a flathead screwdriver into one and twist, this will break the suction seal and let it come off.