Annatinks

I own a Citroen C5 Ultimate Exclusive HDI 2004 model. (I'm told the ultimate just means it had all the optional extras at the time of sale but who knows...) The display is pretty much the same as this one in the picture. It's at the top panel that has the clock lit when the ignition is on. It has both a clock face and digital reading. I have read and re-read the handbook and I can find no guidance on how to change the time which is currently set wrong! Please help, it's driving me mad! http://static.cargurus.com/images/site/2010/09/28/08/18/2001_citroen_c5-pic-8951277129987236998.jpeg