Toliet flange

I am in the process of repairing my leaky toliet and cant figure out how to replace the flange (one slot where the rectangular bolt goes is broken and the other side is bent). The toliet that needs to be repaired is located on the second floor and when water supply is turned on to it, it leaks down into the kitchen. Here is what I have done so far: 1. Replaced the supply hose (I was told by the Landlord that thats where the original problem was), still leaking. 2. Replaced the flush valve, washers and seals. (still leaking) When the toliet was just lifted off the floor, not even having to unscrew the floor mounting bolts. Thats when I discovered that the flange needed to be replaced.The subfloor seems to be water logged. It s wet and cab be flaked up with a screw driver.HOW CAN I REPLACE THE FLANGE. It is made out of black PVC.Do I have to take up the subfloor to get to the flange? Is the flange connected to the PVC pipe? Will I have to cut the PVC pipe in order to get to and replace the flange?Please help!