boil the old backing with pad material, remove carefully with pliers or similar, then push a small 1.5mm/2mm allen key through the holes in the back topush the pad material out. To replace the material, clean out all the old superglue from inside the backing, thinly coat the new compound and the backing with crnoacrylite superglue. As this is a contact adhesive, the old mantra of less is more applies here , so apply sparingly. Leave to dry under pressure, ideally in a vice overnight. Or, have a look at the Heatsink Pad Fitting Guide