Jack up the back of the car and look into the top of the wheel arch.
You will see three 10mm plastic nuts. One near the front,
one in the middle,
and one near the back,
The nuts can be removed as normal using a socket and ratchet.
The liner can then be pulled out of the arch in a down and outward motion.
If you have after market side skirts fitted you may have to remove the arch fitting screws for the skirts. Bend the corner of the liner away from the skirt so it can slot from behind it.
Fitting is the reversal of the above, ensure that everything slots in place as the fitting can be tight and awkward around the top of the shock absorber mounting.
Cheers to Tiny for pointing this out. The plastic nuts holding the arch liner in place are the same as the nuts used to hold the rear lights in place. If you lose one of the rear light nuts you can borrow one from the centre of the arch liner until you get a replacement.
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