I cannot update my phones software

To update an iPhone - the iPhone Must be connected to a Reliable and Stable WIFI AND be connected to Charger. iPhone >> Settings >> General and Software Update. Inside the Software Update, you can activate Software Update and if any new updates are available it should present.

Make sure the iPhone has enough Empty Space for the Update to download, expand and install.

If no updates are presented, then the iPhone is already up-to-date OR it too Old to update beyond what is presently installed.