Sometimes the stereo unit has a 6mm threaded stud on the back with a retaining nut to stop the unit being removed. You have to gain access to the rear of the unit somehow. Cant imagine how! Just looked on the LR manual, its the same info as posted already.
If its a standard LR unit then it SHOULD come out. Are you sure you have pushed the pins right in as far as they go and felt the retaining mechanism being released? I know mine which is standard just pops out. Dont think you should have to dismantle the interior just to get a stereo out!