By Gene and
Step 1 : Disconnect the water supply
Turn off the water to the faucet and place a bucket at the water supply tubes beneath the sink or on the floor to catch any water. Then disconnect the water supply tubes that are attached to the adapter at the wall by twisting it by hand. Use a basin wrench to remove it from the sink.
Step 2 : Loosen the pipe stub
Use a pipe wrench to hold the pipe stub (in the wall) stationary and then unthread the adapter with an adjustable wrench.
Step 3 : Prepare the threads of the adapter
Clean the threads of the adapter and then brush a thin coat of pipe joint compound onto the pipe.
Step 4 : Install the new stop valve
Thread the new stop valve onto the pipe stub and tighten it with a wrench until it is snug. Then connect a new flexible stainless supply tube to the shutoff valve. Attach the other end to the faucet.