The manufacturers default is normally written on the bottom of the router.
As your using that address, this is a Netgear.
I normally login with browser to http://192.168.1.1
with defaults of
Username : admin
Password : password
For best performance and security, ensure your using WPA2+AES and a 12 digit encryption key that uses upper and lower case alpha-numeric and special characters and change the default admin password.