I Need Help Changing my wi-fi password on Teracom Modem

I would like to change my WiFi password on Teracom modem but it fails. Whenever I go to 198.168.1.1 and type user:admin and pass:admin. but the same error dialog box appears: " you have inputted the incorrect login details" I have even enabled WiFi so it could be broadcasted, and re-entered the SSID , but this has not worked too. Please help?
