From your own extension dial *17 to log into your mailbox. For more information, see Logging in to your Mailbox.
When you hear the voice prompt, dial *04.
When you are prompted, key in your current access code. If you do not have one, press # (hash).
When you are prompted, key in the new access code.
When you are prompted to repeat your new access code, key in the new access code again.
When you hear, the message Your access code has now been changed, hang up.