I am helping a friend replace a toilet and the new one does not bolt up to the old flange. Will using a spanner flange solve this problem? If not we are preparde to cut it out with an inside pipe cutter (It is PVC). If we need to cut it out what is the proper method of using the inside cutter. It has the look of making more work than necessary if not used properly. Any help would be greatly appreciated.

Whoa, stop. Why doesn't it fit?

Assuming that your inside cutter is the cutter wheel/drill type. Just don't lose the bit down the drain. You want to cut as straight as possible and as deep as possible directly on top of the existing pipe cutting into the sidewall of the flange. Most cutter wheels are too shallow for this and will require a couple of passes. Dremel sells cutting wheels that actually do the job better. Once the flange is off, you should have a piece of pipe and the hub of the flange glued around the pipe. Keep in mind you may need to clean off any tapering plastic leftover from the flange tapering. That hub you're looking at will glue securely inside of a 4"(street) or (spigot)flange. Before you do all this, you need to determine that it is in fact a 3" closet flange hub for this to work. Street or spigot is pipe size and fits into a 4" or 3" fitting. If it is a 4" closet flange, you can buy a compression flange that compresses inside the 4" pipe. I hate these, but if you have decent flooring to screw to, they will last. One more thing, a 3" regular hub flange will likewise glue inside of a 4" piece of pipe. You just need to cut farther below the floor to allow for the flange taper. Anything else is less permanent, questionable and could cause water damage. Note: If you have access, the best way is to cut out the elbow and replace below the flange bringing up new pipe for a new flange.