How can I update my iPhone

Hey there,

what happened when you try to update your iPhone?

See>>>Update your iPhone, iPad, or iPod touch - Apple Support

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if you have trouble with update See>>>If your iPhone, iPad, or iPod touch won't update - Apple Support

if you have iPhone 6 or less you can’t update it to newer version the last update for this device is iOS 12.5.5

What phone? What is the current iOS version? What happens when you try? Any error message?