Please update my phone version 15.6

Assuming you have a compatible device, 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. 

Hey Mdhaidarali786,

Apple support neither Apple Community cannot update your system remotely.

To update your iOS version follow this article - Update your iPhone, iPad, or iPod touch - Apple Support

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Stay safe & have a great day.

Eric

An iPhone model 6 or 6 Plus cannot support iOS versions beyond iOS 12.5.5, because of hardware (CPU/RAM) incompatibility, sorry.

Regards

Giulio

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