I'm probably quite late in the game here but when I took the fabric off my chairs, I used my steam iron to slowly melt the adheasive. I think it also melted the polyurathane foam a bit too which helped with it's removal. If that doesn't work, take off as much as you can then cut the foam away from the fabric with a sharp Exacto knife from in behind. You will want to do this anyway if any large chunks of foam start pulling away.
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