How do you remove and replace the rear sub woofer on my 99 jaguar xk8?

You've not said if coupe or drop-top, coupe is easier. Lever off speaker cover in centre of window, once one corner is off the rest come away easily, then there are I believe 9 small nuts that need unscrewing, once undone you can open the boot/trunk and carefully pull the sub away. Very difficult to find a replacement sub of the same shallow profile though so easiest to get a used OEM where possible.