In order to change the DSC Powerseries PC1555 system master code, you will need to know the current 4-digit master code. The default master code for the PC1555 is 1234. Go to your keypad and hit * 5 > current 4-digit master code > 40 > New Master Code > #.

 The DSC PC1555 is no longer manufactured by DSC so if you are looking to upgrade to a new alarm panel you can use one of the new DSC panels such as the DSC PC1616, PC1832 or PC1864 security systems.

DSC Powerseries PC1555 FAQ's 

DSC Powerseries PC1555 Alarm Monitoring Options