This article describes how to change the voicemail password.
INSTRUCTIONS & INFO
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.
From the home screen, tap the Phone icon.
Swipe down from the status bar.
Tap Visual Voicemail.
Tap Change Password.
Tap the Current password field, then enter the current voicemail password.
Enter the desired new password in each of the indicated fields, then tap Submit.
Alternatively, from the dialpad dial 611, then follow the in-call prompts to reset your Voicemail password.