To change the default password (1234), you must use the smartphone app (GSM Control) and follow the steps below:

1) Open the app and navigate to the third page. There you will find an option labelled "Disarm Code" 

2) Press it and insert the new password. Afterwards, press "Done" on the top right corner of the screen.

3) This process will create a message that will be sent to your alarm, changing the password.

Keep in mind that this new code will also be the one to use when pairing new accessories with your device!