1. Open the “Settings” system app.
  2. Go to “General” then to iPhone Storage/iPad Storage.
  3. Locate “iOS NUM/iPadOS NUM” in the list and tap on it. NUM represents the version number (example: iOS 13/iPadOS 13).
  4. Tap on “Delete Update” and confirm you want to remove the update from the device.
  5. Download the update again. Install update when ready.

Alternatively, you might want to check “Offload App” on apps so that you can make enough available room for the installation.

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