How do I remove the locks on my 1998 Transit ?

Hello,
I have a 1998 Ford Transit and the barrel on the drivers door will no longer work with any of my keys. I want to replace the lock but can't remove the spring clip from behind it as it is obscured by a steel plate which is fastened to the window runner. Does anybody know how to remove the lock or where I can find instructions to do so ?

Thanx.