how do i replace ignition switch on peugot 406 S reg?

my key got stuck in peugot 406 after some gentle persuasion and WD40 i managed to get it out but now it wont fire when you try to start the car the barrel now appears to work fine i was advised to get new ignition switch that fits on the end of the barrel so i need to know how to fit it any help is a bonus many thanks Ivor P