IPHONE 6 32GB SOFTWARE UPDATE REQUIRED

You only have 32GB of total storage space on your iPhone 6. Is your iPhone functioning properly with that little storage space? Just checking. You will need at least 6GB of free space to update your iPhone over a Wi-Fi Network.

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

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That is NOT possible with your iPhone 6. Your iPhone 6 can only be updated up to iOS version 12.x.x. Your iPhone 6 is limited by hardware and will not be able to run the newer iOS versions. There is no other alternative.

Axel F.