Check for the small key shaped tool to unscrew the bolts in your tool bag/box. Use that diver to unscrew all the screws holding the stereo in the dashboard. If you don't have the tool to unscrew it, you can take it on rent on any of the car accessories shops. After removing the screws, slowly take out the stereo from the dashboard, and loose all the wiring connecting to the stereo. Just make sure that when you unscrew the stereo, your system is turned off.