Authentication mechanism to access WIFI required

I have a BSNL broadband connection with a Type-4 modem (modem MT841). I want restrict access to WIFI using some authentication mechanism. Is it possible to set it or will it be possible to change the router IP from 192.168.1.1

^ pls see Configure Wi-Fi security

Do it as mmm showed you.

It is very important you stop unauthorised access to your connection coz as you can imagine any one living near you or a passer by can just log into your network and do anything may be a small time paypal fraud or anything really or may be your next door might run a few torrents using your limited connection and run your bills into thousands

^^^^ thats why i dont trust wi-fi....

a similar thing happened to one of my frnds....

The link provided my mmm is great. I do have one of the links stored in my favourites that i am sharing with you.
Its Complete Guide to Wi-Fi Security
Hope you find all information about it

^ thanks Rajat for the link to a useful guide .