Trying to install a new shower head. The old shower arm coming from wall is not a regular arm that has threads on it. The end of the arm has a round ball ,with a threaded cap.The cap comes down to the ball then the shower head is attached with the head going over the ball then secured by the threaed cap. Need to put an updated shower head on but cant find one that will fit this type of shower arm. Do I need to remove old shower arm and intsall a new one. Have no access to see how the parts are installed inside the wall.