It is recommended that a medical professional remove a cast as first the cast may not be ready to come off and secondly you may hurt yourself in the process requiring more medical attention. As plaster is more water resistant than a plaster cast it is not recommended that you try to soak it off with water as this will not work. If you do intend to remove the cast by yourself you will need the following items:
A second person
A pair of tin snipes
In order to remove the cast you will want to lay the extremity on a flat surface and the secondary person will want to use the tin snipes to cut from one open end of the cast to the other, being careful not to cut the skin. You can then spilt the cast with your hands and remove it.
After you have cut through the fiberglass you will see cotton padding, use the scissors to cut the cotton padding off.