How to update iOS over mobile phone data

At this time, a Wifi connection is required to update iPhone OS. One work around would be using a different device and making a hotspot, though be warned, download speeds can be slow over a 4G network. I would recommend that you just update over a stable Wifi connection.

(Friendly tip) I also recommend the iPhone being plugged in during the update process, as loss of power during updates can result in corrupt files.

You cannot, you have to have wifi at least or be connected to a computer.