First I would try to vacuum them out. Take the defrost vent cover off. It pulls up. Take a shop vac and duct tape a section of garden hose or similar hose that will fit in the vents and snake it in there and try to suck up the candy. If that doesn't work you can try taking off various pieces of dash to get to the vents. May have to lay on your back with a light and see if you can pull apart the vents at the connectors.