I am replacing a 20 year old radon fan that is vertically connected top and bottom to pvc with fernco couples. I have removed the bands but there is no slip up or down to pull the o;d fan off. I have new fernco couples to attach the replacement fan.

So ...
Question 1: How do I remove the fernco already installed?
Question 2: Will there be enough of an opening after removal to install the replacement?

roll the rubber back onto itself opposite the fan

then a little muscle to spread the duct/pipe

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

If they had metal wraps around them and they are still soft enough, you roll them down like a stocking. Otherwise you slit them to take them off, then put the new ones and and roll them down, slip it in place, then snap them back straight and tighten the bands.

I really appreciate the suggestions, but the rubber thickness and stiffness of my couplings makes it impossible to roll down. Perhaps the fernco brand is easier to roll down than the so-called "flexible" couplings I bought at Lowes.

Right, you need to take those back and get the ones that have a stainless band that covers the entire rubber portion. Use a razor knife to cut the old rubber away from the pipe.

Actually, if they are the heavy tubular ones with just hose clamps on either end, you can slide them down the pipe, (you may have to tap them with a hammer to get them to move).