The long pending update that the iPhone users were waiting for is here. iPhone 5 and 5S users had lost the ability to toggle between 2G, 3G and LTE networks with a previous update. This was a real disadvantage when it came to battery life with users having to charge their battery atleast twice a day due to consumption of battery by 3G/ LTE cellular data.
Although apple has provided an update, it is up to the network carriers to provide the accessibility to the user to update the carrier file. Airtel in India has given an option to update the same and as you can see below after the update it allows you to toggle between networks. If battery issue was stopping you from going for an update, go ahead and update.