A replacement shock absorber has Part Number
Q000 9225 V001 0000.

There can be a couple of reasons for needing to change a shock absorber, whether the bushes have perished, or the shock has failed.
Remove the wheel, chock the front wheels and jack up the back of the car.
Remove the wheel arch lining. It is held on using 3x 10mm plastic nuts, and 'tucked' into the panel and body.
(The rear panels are removed in the picture)





The shock absorber is held on with 2x E14 bolts, one at the top, one at the bottom, and can be changed without lowering the subframe down.


 

Remove the lower E14 bolt first.
It is secured (usually) by a captive nut, so you don't need to use a spanner.
It has been known for it to be a separate nut though, so have a 16mm spanner handy.

Remember the shock is in a state of compression, but it's not like a spring, so it won't 'fire' out of the mounting.



Remove the top E14 bolt, and secure the nut using a 16mm spanner/socket.



If either the top or bottom mounts are stuck in the mounts, they only need a little tap to free them up.



It should now just come away for you to replace.
You may need to ease the new shock into the mounts and finely adjust using a pry-bar to line up the bolt-holes.