I can tell you how to change the code on a Citroen ZX if they are the
same - I don't know, but it might be worth a try!
Unlock car, then type in four digit code; the light goes green, then
immediatley enter a fresh four digit code. Turn key off, and lock car
again, then unlock car, and use new code. The old code is also still
active until you activate the new one sucessfully, so don't panic if it
doesn't work! Point to note - I don't know if it is the same as the
ZX, but if you call your local citroen dealer, they will be able to