How do I save a radio channel on my N reg Nissan Micra Blauplunk radio/mp3 ?

I have bought an N reg Nissan Micra and it has a Blauplunk radio / mp3 player (I think, it doesn't take a cassette) and when I tune in a station I don't know how to save it as I don't have the manual. Can someone help as I'm listening to whatever I can tune in to and would like to save each channel to the memory buttons.