Step 4 · Demolish Old Valve
Working from your access panel, identify the hot and cold supply lines and the pipes leading to the shower head and tub spout. Using a tubing cutter, cut the hot and cold pipes below the old valve body, and cut the shower riser and tub spout pipes above and below the valve assembly. Be prepared for some water to spill out. Once all four pipes are cut, the old three-handle valve assembly should be loose and can be removed from the wall cavity. Wear safety glasses during this step.