Help needed for 2003 micra

Hi, The Wife bought a second hand micra last week, a great little car but the only problem is the radio & cd player. The buttons on it seem to have a mind of their own. (when you press the eject button the sound goes up and when you press the volume button a radio station might come on etc,.) In other words its bunched. Now my problem is I am going to put another radio in and I am not sure how to go about it. Any help would be much appreciated. Ray.:runaround: