How can I update my software without WiFi

As Ckuan mentioned in the response above, you cannot update your iPhone over the cellular network.

If you do not want to use WiFi to update your iPhone then have another option and that is to update your iPhone with the use of a computer. Please click on this link which will guide you ➔ How to update your iPhone (Scroll down to the instructions - Update your device using your computer.)

The thing is that you will still need a connection to the internet for your computer.

Axel F.

You can't, Wi-Fi is a requirement.