How to update the software on my iPhone 6?

To update to the maximum of iOS 12.5.7, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

Your iPhone is too old and would not be compatible with the newer software updates.

Click ▶︎ iPhone compatibility with iOS 13 for the complete list.

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