new code

My friend has a 87 maxima. He wants to change the the door code because he got it from a used car lot(it's payed for). It all so has an alarm that he needs to disable because he don't have a remote for it. there is also a button by the E-brake. does anyone know anything about how to or what the button is for. thanks for any help.

My friend has a 87 maxima. He wants to ... there is also a button by the E-brake. does anyone know anything about how to or what the button is for. thanks for any help.

Buttons change depending on market and outfit, year model. I have three: viper for front lights, antenna, rear fog light.