You may have to pay up for an engineer on this one.
This is a frost free appliance so unless you want to get involved in removing the evaporator cover, checking the ice build up, defrost heaters, air vents, fan etc I would recommend calling your local engineer. (most local engineers are cheaper than Electrolux).
Finally remember if you are going to defrost the appliance 24 hours may not be long enough, the ice build up may be a few inches thick and ice cube consistancy.
be safe switch off if your going to get tools out!.