No iPhone 6 update

See If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support. If you're trying to update over the air try using iTunes or Finder instead, or vice versa. If you have an older device it may already be running the last version of iOS that it can support.

tt2

The iPhone 6, released by Apple 8½ years ago, cannot be updated beyond iOS 12.5.7.

AnkitApp wrote:

why you should nit give an update in iphone 6

The processor is too old and the memory is too limited.