Generally routers have own admin control panel (generally via web) where you can setup configuration, parameters, watch router status etc…
They have a default username and password (this last can be modified then), in the case you lost or you don’t remember the login here a list of sites with various routers and their default logins:
Router Passwords
CIRT.NET
port forward
To know the address to access it you simply must know the IP address (naturally a private address) of the gateway. Let’s see how to find it in the case you dont know it.
In Windows: open a DOS console and type “ipconfig” command
In Linux: from shell type “route” command
In Mac: from terminal type “netstat -nr” command
Suppose the IP address you have found is 192.168.0.1, so to access the router admin panel we must to type in our preferred browser the address http://192.168.0.1