How to convert LED TV to smart TV?

You can opt for the following devices for the purpose of converting your TV into a smart TV. Please note that many of them are not available in India. Here is the list of few brands -

1. Google Chromecast
You can get it from eBay India or Amazon India for about Rs.4000. You just need to connect the device to the HDMI port of your TV. The device needs to be connected to the USB port of your TV or any other power source. Switch to the HDMI source on your TV and follow on screen instructions to configure your existing WiFi. Install the Chromecast app on your phone or laptop/PC. Run the app and connect it to the WiFi network. Link your device by following the instructions from the app.
Once done, you are ready to use the smart TV functions.

2. iOmega ScreenPlay
This is a box type media player. You can get it at a price of around Rs. 13000. You can use it to access some preloaded content like YouTube, Flickr and others. It also includes a browser to surf te Web.

3. Amkette EvoTV
It is available in different variants at prices ranging from Rs. 5000 to 11000. This is an Android box. Apart from the browser, it also lets you access apps from Google Play Store. You can also add your own list of apps to the already installed ones. A USB keyboard can be attached to the box.

Google Chromecast is currently available for under Rs.2699. As Timmappa suggested above, I think it is one of the best devices currently available for converting a normal TV into Smart TV.

Alternatively, you can also look at Tewee 2.0 which offers additional features.