How do you input radio code on Peugeot partner van?

I have a 51 plate Peugeot Partner van with a standard radio. The radio code should be a 4 digit code with each number having the value of 6 or less. The code is entered using just the 1-6 radio channel numbers, and that's it no need to press any other buttons the radio should just spring into life!

Good luck

Tommo