Hi!
The ball is bolted to the hatchback door. The part itself is a ball on one end, that comes down to a hexagonal section (for screwing/unscrewing purposes), and a threaded shaft. If I remember correctly (I replaced mine 2 years ago), you should be able to just knock the piston towards the center of the car so that it pops off the ball. I think mine wouldn't come off so I just unscrewed the ball and replaced both ball and piston. I THINK the ball was around $7. After installing new ones on the car, I greased them up (including the socket in the piston that the ball goes into) and popped the new shocks in place. Hope this helps!