I have chatted and talked with customer service about changing password for my modem and router. Nothing they told me to do worked. So I wanted to connect my smart phone and internet together. Did not work.
If you are referring to the router and do NOT have the exede speedboost you might want to contact the manufacturer of the router (linksys, Cisco, etc). This is a pretty basic way to change the WiFi password: http://www.wikihow.com/Change-Your-Wi-Fi-Password