Each router has a web-based administration panel in which you can administer important network parameters. Here you can make changes to WiFi name, passwords, set up a guest access and do other pertinent changes. As various brands have varied default IP addresses and mode of logins, the process might be different according to your router.
The following is a list of the popular router brands. Select your brand to get some specifics about how to access and log-in to the settings page of your router.