You can use the following process to change the voicemail password of your mailbox. If you have forgotten your password:
If you have an Avaya phone that supports visual voice, you may be able to change your voicemail password through the phone's menus. See Visual Voice.
If you have access to the IP Office user portal application, you can change your voicemail password through that application. Refer to Using the IP Office User Portal.
Otherwise, contact your system administrator.