From your keypad, press *5, then enter your current 4 digit master code (you should get three beeps, if you get ONE long beep then you are not entering the correct master code), then press 40, now enter the new 4 digit master code you wish to use, press your # key twice. To test the new code, enter the code twice on your panel. This should initiate the arming process & then will disarm the system.