Open Settings
Tap General
Tap iPhone Storage
Find the iOS update file in the list
Tap the update file
Tap Delete Update
Confirm deletion
Turn off Automatic Updates in Settings
Tap General
Tap Software Update
Tap Automatic Updates
Disable Download iOS Updates
Disable Install iOS Updates
If the update is already downloading, turn on Airplane Mode to pause it
If the update is already installed and the device is restarting, wait for the process to finish
If the update is stuck, restart the iPhone
If needed, erase and restore the device using a computer to remove the update