1. Pull the two side bands, starting from the bottom edge.
2. Remove the four screws.
3. Unlock the three interlocking snap in at the top: push the tabs with your finger while you pull the frame.
4. Pull the radio block, releasing the four mounting pin-push (pink color).
5. Release the three connectors and the antenna plug.

There are five buttons at the steering wheel: volume +, volume -, channel up, channel down and mode. At the radio connector there are only three wires connected to the 20 pin harness.

Here it is the schematic: