Use a flat head screw driver, go into the boot and behind the light there is a hole in the carpet.
If you put you finger in you will feel a plastic nut/screw thing - stick the screw driver in there and turn away - be carefull that the screw does not fall off the screw driver
thats the easy part - the side of the cluster is held on by 2 pins which can be a bit awkward to remove, just be patient and work at it - try get your finger tips between the bodywork and the light cluster
once you remove the light, proceed to remove the mains clip and then its easy enough to work out how to remove the backing plate of the cluster