Press the spring down on the wire or metal frame. The loop at the top can slide down to a point where the wire or metal frame is narrow. It can then be turned slightly and popped off. Be careful and release the spring slowly so it doesn't fly off. To install simply push the spring and wire or metal frame through the hole from the bottom, depressing the spring and re-install the top loop on top of the hole. Hope that makes sense.
Four Corners Unit