How to swap original radio for newer one?

Hi there,
Lady in distress!!! Please bear with me as I know nothing about cars but still would like to try and do this myself! I've just bought a Xsara Estate 2002 and would like to change the original radio cassette for my own Radio CD unit. How do I actually removed the radio (without damaging anything)? Does the whole unit with the display screen need to come out or can I just take the radio out? I have connected new radio units to older cars before but what can I expect to find in a newer car with lots more electrics?
Many thanks