1. Connect using a web browser. When you are first configuring your router connect it to a computer via Ethernet cable. This will ensure that you are not disconnected if changes are made to the wireless network. Open any web browser and enter in the router's address into the address bar. Virtually all Linksys routers can be access by entering the address 192.168.1.1. If you cannot access the router from your browser the "web management" option may be disabled. If this is the case press and hold the Reset button on the back of your router to reset it to factory defaults.
2. Enter your username and password. When you try to access the router from the web you will be asked for the username and password for your router. These vary from router to router but the defaults should be listed in your documentation. If you can't find it you can reset the router to factory settings and then look up the router model online. Most default usernames are "admin". Most default passwords are "admin" or blank.
3. Use configuration software. Many newer Linksys routers come with an installation CD that can install a configuration program. This will allow you to change settings without having to connect through a web browser. You typically will not need to enter a username and password to use it. Once you open the configuration software the menus will generally be the same as the browser menus.