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.
You can change your voicemail password by tapping the Phone tile from the Start screen.
Tap the Voicemail icon.
Enter your current password (if prompted) > From the main voicemail menu, tap the 4 key > 2 key > 1 key > 1 key.