Step 4 · Remove the Old Angle Stop
This is the most critical step. You must use two wrenches. Place one wrench on the body of the angle stop and turn counter-clockwise. At the same time, use a second wrench to grip the copper pipe coming from the wall (the stub-out) to hold it firmly in place, preventing it from turning. Loosen the large compression nut that secures the valve to the pipe. Once loose, you can finish unscrewing it by hand and slide the old valve off the pipe.