No WiFi available, how can I update security?

If by security you mean the iOS (iPhone Operating System software), then you do need WiFi or connect the phone to a computer which has internet > launch iTunes > and do the iOS update via iTunes from the computer

Note: when you update the iOS, you are installing the latest operating system designed by Apple for your iPhone and in general overall security of the iPhone is improved.

Here are the steps you have to follow for either updating iOS wirelessly through WiFi or through a computer

Update your iPhone, iPad, or iPod touch - Apple Support

JoannaSull wrote:

How can I update security on my IPhone without WiFi?

If you mean IOS update, you need to be connected to wifi in order to update over the air.

You don't.