To change your voicemail password, you must know your current voicemail password. Note: If you have forgotten your existing voicemail password, you will not be able to access Voicemail until you reset your voicemail password.
Tap Settings.
Tap Phone.
Tap Change Voicemail Password. Note: This option will only appear once you have set up Visual Voicemail.
Enter the current voicemail password, and then tap Done.
Enter the new desired voicemail password, and then tap Done.