Sorry for the late reply, I have replaced the shocks on both of my Z3's and it really isn't that difficult.
Firstly pull back the felt lining from behind the roll hoops on both sides you don't have to pull it all out just in the corners. This will reveal the top mounts on the shocks, if you undo both the outer nuts and remove the reinforcement plate if fitted it will be ready for when you jack the rear end up (don't worry nothing will fall off at this stage)
Next jack up the rear end and place on axle stands, you will hear the shocks disengage from the body as you jack up the rear end but don't worry this is expected. Once the car is secured on axle stands remove the wheels after slightly cracking the bolts off before jacking the car up. Once the wheels are off you will then have access to the lower shock mount which is simply a single bolt going through the lower bush, the shock should now be able to be totally removed from the car.
Once the shock is removed from the car you can disassemble the top mount on the old shock and swap over to the new shock unless you are putting new top mounts on which is advisable if they are still the originals. Remember how all the washers go on the top mount as you disassemble and reassemble in the same order. Always fit a new paper gasket to the top mount when you reinstall in the car so you don' have any creaking issues later on.
Offer the new shock back upto the car and insert the lower mounting bolt, then using a jack under the rear hub gently jack the rear hub axle up so that the top shock mount goes up through the hole in the wheel arch Then pop back inside the car and pop the two top mount nuts back (only need to be finger tight at this stage). Lower the jack under the hub and bolt the wheel back on.
Repeat the above for the other side. Once both shocks are on and you are happy you can lower the car off the axle stands and tighten up the top mount nuts once weight is back on the rear axle. Replace the rubber protection dome with the aid of a little bit of washing up liquid it slips over the top mount quite easy. Now all you need to do is put the felt lining back in the retaining groove.
Always ensure you follow all the safety precautions when raising a vehicle off the ground and use axle stands to secure the car and don't soley rely on a jack as a jack could fail without warning.