If it's still connected to the old network/password, you can tell it to forget it this way:
If it's not connected, or once you've told it to forget the network, you just do the setup steps again:
Those steps are listed at the end of the link above.
I just wanted to jump in real fast to see if you saw Byteguy's reply and to see if you still needed some help on this or if you were able to get it sorted out. If you are still needing some help, just let us know and we'll be happy to continue helping.