I was trying to replace a leaky valve in a price Pfister shower control knob but can't figure out how to remove the old valve. Is there a special tool for this? Thanks

I was trying to replace a leaky valve in a price Pfister shower control knob but can't figure out how to remove the old valve. Is there a special tool for this? Thanks
Yes, it's called a basin wrench, (see image) and can be picked up at most hardware or plumbing supply houses. This wrench is used to get at those hard to reach nuts that secure the valve to the fixture. Good luck, Tom