All types of angle stop water valves share a few basic replacement steps:
Turn off the building's water supply.
Open a hose bib, releasing the water pressure in the building's pipes.
Place a bucket under the existing angle stop.
If the angle stop connects to a detachable supply line, grip the existing angle stop with a wrench and place a second wrench on the 3/8-inch compression nut holding the faucet or toilet's supply tube.
Hold the angle stop still and turn the 3/8-inch compression nut counterclockwise until the nut releases.
Remove the supply tube. If the supply line and angle stop are a single unit, remove the supply line from the faucet or toilet.
Remove the existing angle stop, using the appropriate tool.
Clean the debris from the 1/2-inch water pipe's surface.
Install the new angle stop, using the appropriate installation method.
Hand tighten the faucet or toilet's supply tube on the angle stop's discharge port.
Place one wrench on the angle stop's body and the second wrench on the 3/8-inch compression nut.
Turn the 3/8-inch nut clockwise, while keeping the stop still.
Turn on the building's water supply and check the valve for leaks.