the router IP is 192.168.1.1 by default.
You will need the password. If someone set the router up for you, they should know it, but if you never changed it, the default password for the Airport Extreme is %26quot;admin%26quot; (without the quotations) with no username.
Once you are in the settings, you should be able to simply change the SSID from there.
Goodluck:)