I used to have a small refrigerator where the freezer would always ice up real bad and have ice built up several inches thick. I tried defrosting it once and tried to hurry it up but chipping out the ice with a knife. The knife went right into one of the coolant tubes and just like that, all the refrigerant was removed. It was easy. Probably not the recommended procedure though.

You also might try a place that sells and services air conditioners, they could probably remove it for you too.