How hard is it to change the floor flange under the toilet?

My upstairs toilet was leaking. I pulled up the toilet, cut away the rotten wood and still have to replace the floor flange. It looks like the drain itself is PVC but I'm not sure. My house is in the north-east and it was built in '78. I think the toilet and the wax ring are original, which brings up another question: How often are you supposed to change the wax ring, if at all? I have two other toilets. I think one other is also leaking.

The flange I have is rotten to the point that I don't know what it's made of.

If the drain is PVC, you just cut the flange off and glue one on with PVC pipe glue. The problem you may run into is once cut the pipe may not be long enough. If that is the case, you will have to cut the pipe short enough to add a coupler and a short piece of pipe and the flange. If you have a 90 degree elbow just under the toilet, cut the pipe back past the elbow, add a coupler and a short piece of pipe, then an elbow and then a piece of pipe for the flange. Same thing with ABS ( black plastic).

Wax gaskets are usually good for decades if installed properly, but anytime you think it's leaking it should be replaced.

Certainly the SUBSTANCE of the FLANGE may be part of the issue, but you don't state IT'S condition??? Or the notion as to why it may need changing?

PVC was widely used in 78 most especially on upper levels.

First know the substance of the flange, how it's connected to the sewage drain beneath it, then proceed.

PVC can be cut and spliced easily.

WAX rings don't strictly have to be "checked" nor do they strictly "degrade"... IT'S WAX... not at all affected by water,,,HENCE the reason it's in use. The degradation might occur in a rotting floor or a shifting toilet, but it's not at all like a 3000 mile oil change in a vehicle.

You don't state the source of any leak, so it's a bit difficult to assess online. certainly if water intrusion is occuring at the base of the toilet, then you have a more immediate/critical problem, than with a leaking tank. BTW,,, WHERE your house is,,, is of little consequence,, no offense.

Steven Wolf