Update issue

Please review this guide published by Apple ➔ Update your iPhone, iPad, or iPod touch - Apple Support

And

Read the information below if you are planning to update your iPhone over a WiFi Network.

Make sure that your iPhone is setup to meet the following requirements before you attempt to update the iOS version-

• Your iPhone must have a fast Wi-Fi connection; you cannot update over cellular data or a cellular hotspot
• The iPhone can not be in Low Power mode
• The battery state of charge must be above 50%
• Your iPhone must have at least 3 GB or more free storage space
• Your iPhone cannot be connected through VPN
• If you are not planning for it to update automatically you should turn this option off, as it will only update when the phone is plugged in, connected to Wi-Fi and locked
• You should leave the phone plugged in until it finishes updating, both to assure that it remains above 50% and to keep Wi-Fi enabled (Wi-Fi turns off when the phone sleeps if not connected to power).

Axel F.

1. Go to "Settings > General" on your iPhone.
2. Select "iPhone Storage".
3. All the apps will be listed there, including the iOS software update.
4. Click on the iOS update and tap "Delete Update" to confirm
5. Try again to update your iPhone like you have been over a WiFi Network and ensure that the requirements posted in my previous response have been met.

If that still does not work then I recommend that you use a computer to update your iPhone. The procedure to update with a computer is also listed in this guide by Apple ➔ Update your iPhone, iPad, or iPod touch - Apple Support Focus on Update Your Device Using a Computer section.

Axel F.