Link a computer to the router by ethernet cable and type router IP address into address bar of your browser (usually 192.168.1.1 or 192.168.0.1.)
At login box User Name is admin.
Default Password is password (though sometimes different for earlier Netgear models -- see manual).
Password may have been changed from default by user, in which case reset is needed.
Once in either write down or cut and paste the security passphrase and note security type. Also check that Access by List (include by MAC ID only) is not enabled.