How to remove beta software to update iPhone?

Remove the public beta by deleting the beta profile

Go to Settings > General, and tap Profiles & Device Management. Tap the iOS Beta Software Profile. Tap Remove Profile, then restart your device.

How to uninstall iOS beta software - Apple Support

Remove the beta profile, the attempt the update again.

Also: charge the battery and preferably leave it connected to the charge circuit during the update

Also: connect to a WiFi network.

Also: turn off the Low Power Mode option.