Open your Honeywell Vista10P alarm system installation and user's guide to section three, page 5 (it's the 23rd page from the cover. Find the installer codes at the top of the page in the "Entering Program Mode" section.
Open a web browser of your choice and download the Honeywell Vista10P alarm system installation and user manual from the Vista10P product details section of Honeywell's website.
Enter programing mode by pressing and holding the "#" and "*" buttons on the keypad for 50 seconds. Key in the installer code after the system beeps.