Pull off the center cover inside should be some kind of nut or screw. Some may have an allen set screw under lever look at it closley you will figure it out. It depends if it is a plastic handle or a metal one. Good luck
Delta makes four different shower valves depending on whether it is pressure balanced, temperature controlled, rotary handle, or joystick/knob handle. But they all come apart by unscrewing the body nut that is revealed when the knob is removed. But some do not have springs and washers and you have to buy the entire cartridge.