How to updates software

If your iPhone is eligible for an update, check by reading this Apple article: iPhone models compatible with iOS 12 -> iOS 16 -> iPhone models compatible with iOS 15.5 – Apple Support (UK)

Go to Settings -> General -> Software Update -> Download and Install.

You need about 6 GB device storage and good Service and/or Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

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

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

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If the last security updates iOS 12.5.7 , it can’t be update to a higher iOS 13 or later.

Hello,

There are different ways to ensure the highest iOS that your device will support is installed on your device.

Any equipment currently running iOS 12.5.7 can't be updated to anything higher.

An iPhone 5S, 6, or 6plus, will only update to iOS 12.5.7

An iPhone 6S through 7, or SE(gen. 1), will currently update to iOS 15.7.5

An iPhone 8 or later will directly update to the latest iOS, 16.4.1

This support article has instructions about updating an iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support

You can also use Mac and PC computers to update system software --> Update iOS on iPhone - Apple Support

When updating, your device will update to the highest version currently available that it will support, or it will just say it is up to date (and can't go any higher) and won't install anything. Apple indicates ( Unable to update my iPhone 6 Plus from 12… - Apple Community ) I need to point out the obvious and state that if you want to run a higher system version than your current device will run, that you need to buy a newer device.

Note that New Rapid Security Responses are delivered only beginning with iOS 16.4.1 ( About Rapid Security Responses for iOS, iPadOS, and macOS - Apple Support )

For a list of equipment supporting iOS 16 and iPadOS 16 (and the current 16.4.1), read this article --> iOS 16 and iPadOS 16 are compatible with these devices - Apple Support

"Software" includes the possibility of apps too:

For apps on a mobile device --> App Store app > Updates, or select your icon in the upper right corner > click update all or scroll down past the first screen to select individual apps.

Plenty of instructions above.

Update your iPhone or iPad - Apple Support

I need to upgrade my phone