How can i move a PIR on a Vertitas R8 system?

Hi!
I have a Veritas R8 alarm fitted to my house and due to a extention im carring out i need to move a PIR into a different location. Please could you advise as to the correct process in which to take.
Im aware that the PIR has a tamper mechanism under the cover and know the system activates when touched. I would like to know the correct procedure for disconnecting the PIR so i can extend the cable without disturbing the neghbours etc..
Many thanks and i look forward to any help,
Regards,
Colin.