Gently pull on the top of the joystick until the cap comes off of the joystick.

The cap might not detach from the touch sensor spring. In that case, let the spring remain attached to the joystick cap and don’t forcibly remove it. If you do this, it's very difficult to reattach without damage to the spring.

There is a spring that's located between the joystick housing and the cap. Don't bend or break this spring as it controls the touch sensor.