The best thing is to replace it. You change the setting code by pushing "PROG" then entering the engineer code. There is a default engineer code which I will not publish for obvious reasons but if you google it, you should find it. The Installation manual [30 pages] can obtained similarly. If you just want to change the customer code press 8, 2 and dependent upon the whether your installation has a remote keypad or not you'll either see 4 LEDS "on" or the no. 4. Enter your new code. Then press RESET to return to DAY mode. If you want clear all settings and return to the factory conditions press SET, SET. Your customer code will then be the default one. The latter course may be necessary if the alarm company has changed the engineer code. The latter action will return the engineer code to the default one.
Mick
March 2014