Usually the 2 holes each side of the unit are filled with security screws. You need a small Allen key to remove them.
Then you need to get long thin prongs down each hole about 3 inches.
mall screwdrivers are good if you don't actually have the correct tool. The unit shuld them pull out.
The above answer will work, but a much quicker way of removing the stereo is to simply leave your car parked anywhere in the Liverpool area for a short time, It will be out in minutes!!!