Why does my car stereo change stations at ramdom

First thing to check is if your radio has an auto scan function or auto preset function. These kinds of "auto" tuning functions are designed to play a station for a little while and then scan to the next station. Tapping the button for this function usually stops the scanning. The function might be labeled something like "seek", "auto", "travel", or something like that. If there doesn't appear to be any auto tuning function going on, next thing to check would be the steering wheel controls wiring to make sure the radio isn't erroneously getting a next station or "station up" command from the steering wheel.