Want to change faucet in the bathtub there is no shut off at the tub there is a pressure tank in the basement and a small pressure tank at the pump outside. Can someone help me I am pretty handy. I know I have to drain the system but I am just unsure of how to do this.

You don't have to drain the system.
Simply shut the pump off at the breaker box and open a faucet to bleed off the pressure. Purchase the valve you wish to install and tell us about your present hookup and one of our experts will walk you through the installation. Good luck. Tom