You will have to use the Administration section of your router to set the wireless settings. The password you have to enter is the one set in the router. Connect to the Admin interface, go to Wireless > Wireless Settings, then rename the SSID of your WiFi, and change the password as well. After this procedure, use your phone and connect to the new network, input the password and that's it. If you can't access the Administration interface, use the manual of the router to learn how to access the Admin area.