Dont know how to use Veritas R8Plus alarm?

I've just moved into a house with a Veritas R8 Plus alarm system. There are no codes for us to use to either set/reset or change codes to allow us to use the alarm. Can anyone help or let me have an easy to use guide on how to sort this out? I've looked at the Texecom user guide but this is not clear (to me). Thanks. David