Here is the end that is fastened to the car. It has a black plastcup on top, which is just to pull of.

Here is the end that is fastened to the tailgate.

Replacing the gas springs

New gas spring + the old attachment

Get someone to hold the hatch while you disassemble the gas springs, or let it hang by a string that you mount in the ceiling, if you have the car indoors.

To get out the metal bar that keeps the ball in place: The bar is said to be possible to pry out of the little hole.
But soon you find out that this is impossible, and ends up breaking up the whole thing.

New gas spring + new attachment

If you install new attachment, it is just to screw it in place, add grease, put the ball inside and close the hatch. Then the ball is pushed into place by itself.
(It can ogso be that this is the way to get the ball out; push the hatch further up when it's open, but this I have not tried.)

The best would be to buy both new gas spring and a new attachment when replacing.

If you are lucky, you will manage to get the ball out without too much being destroyed.

Or you will end up like this...

It is possible to hook on the metal bail that was inside this way, it can be enough to lock the ball.