Ok to defrost this appliance what you need to do is empty the freezer and remove the drawers.
Then go inside the fridge and turn the dial to 0.
This will then turn the appliance off.
Then the you need to either leave it for 24 hours or get bowls of boiling water and place them on each shelve inside the freezer and this will start to defrost it quicker.
What ever you do don't use a knife or anything like this to break the ice off as this can pierce the evaporator and if this happens you need to replace the appliance as that cannot be replaced.
So do the above and you can then defrost it that way. If you need anymore info just get back to me.