Hang on to the actuator at the bottom and remove the C clip. Be careful; the spring may want to launch either the shaft or the actuator!
As you slide the shaft out, keep track of the order of the parts and whether they come from the top or bottom of the joystick. There should be an actuator on the bottom and a spring, spacer, and dust shroud on top, but that's based on my experience with Happ joysticks, yours may have an extra spacer somewhere...
--Chris