Changing Zones on an Optima XM alarm system?

Hi

The alarm is currently set with the zones for entry through the front door. We want to enter from the back door.

When we enter through the front door, the alarm bleeps and there is a delay long enough for us to enter the code to turn off the alarm before it sounds.

If we try to enter through the back door, the alarm goes off instantly - there is no delay to allow us to turn it off.

Does anyone know how we can change the zones/settings to allow us to enter through the back door?

Thanks
Jen