HI

I just come to know that I need to access my modem which is Beetel 450TC1 through its admin setup.But I don't know where it is and how to access it ?

Connect your modem to your computer through lan cable and make sure computer is set to receive IP automatically .
Now open your internet browser, firefox or any other, type address : 192.168.1.1 and then if everything is fine, it will ask password and username, give both as admin / admin and you should see interface to manage it. If you are still unsure then read documentation came along with your router.

I don't know where it is and how to access it ?

Have you connected your modem to computer using LAN cable ?