A great website for finding the user manual and technical details of a router can be found here. Although it is an Australian website it covers most common routers sold worldwide.
Just scroll down the list of manufacturers to find your router and click the model name to reveal the specifications of the router including the type of wireless security supported, the speed of ADSL, the speed and type of wireless service and (under the Configuration section) the default administration username and password – needed to access the router’s configuration pages.
In most cases, the Support section at the bottom of the page provides links to the manufacturer’s website, user manual, datasheet and firmware updates – very handy if you have lost the user manual as some manufacturer websites are not easy to navigate, especially with older legacy routers.
If your router is not listed and you just need to find the default administration username and password to access the router, try the Routerpasswords website and select the manufacturer of your router then click ‘Find Password’ to show a list of their routers with default usernames and passwords. If your particular model is not shown then try the username and password for a different model by the same manufacturer.
Tip: Manufacturers often use the same username and password for most of their routers aimed at home users e.g. D-Link typically use admin and admin, Netgear typically use admin and password.