How can I adjust the entry-delay of ITEC Horizon 1500 (Microtec)?

I have a perfectly working (rather old) home alarm. Three months ago we moved into a new house, I took the alarm & belongings along to the new house. We now haven't got a zone without a PIR where I can fix the remote keyboard. So as I enter the house the alarm goes off before I can de-activate via the keyboard. How can I manage to get a 10 or 15 sec. delay ?? Thanks !!