How to upgrade your old Airtel sim to 4G
Go to http://www.airtel.in/4g/sim-swap Request for your Free 4G SIM after you receive the sim you can find 20 digit sim no on the back side of sim packet or sim itself send sms to 121 message as followed SMS YOUR20DIGITUNIQUESIMNUMBER you will get a message press 1 send to confirm you will get a confirm message ,Now you have to wait until your network goes down ,after network goes down you can swap with your NEW 4G SIM go to settings and change your network to 4g Enjoy 4G :)