why are you not update my iphone

It could be that your iPhone is too old to update any further, check this compatibility list

The iPhone 5S/6/6plus cannot update further then iOS 12.5.7

The iPhone 5C cannot update further then iOS 10.3.4

The iPhone 4S cannot update further then iOS 9.3.6

The iPhone 4 cannot update further then iOS 7.1.2

The iPhone 6S/6Splus cannot update further then iOS 15.7.7

The iPhone 7/7plus cannot update further then iOS 15.7.7

The iPhone SE (2016, first gen) cannot update further then iOS 15.7.7

If you'r iPhone is compatible, please go to settings>general>software update. Make sure that your iPhone is connected to a wifi network and that low power mode is turned off.

If you cannot update wirelessly, please update via a pc or Mac instead

Update your iPhone using a Mac with macOS Catalina or higher

On a Mac with macOS Catalina or higher, you will use the finder in order to upgrade your iPhone. Make sure to Back up your device before starting the upgrade process.

On a Mac with macOS Catalina or later, you will follow the following steps:

1. Open a finder window
2. Connect your device to your Mac via a lighting to usb A or a lightning to usb c cable
3. Select your device in the left sidebar of the finder window
4. click general, then click check for update
5. Click download and update.
6. If asked, enter your iPhone passcode

Update your iPhone via a Mac running macOS Mojave or earlier, or on a Windows PC

On macOS Mojave or earlier, or on a windows machine, we won't use the Finder to upgrade your iOS

Instead, we will use iTunes. Make sure to Back up your device before doing any update or upgrade to your phone.

1. Open iTunes
2. connect your device to the computer with an lightning to usb a or a lightning to usb c cable
3. Click device button in the iTunes toolbar
4. In the summary tab, click check for update
5. Click download and update, follow The on screen instructions
6. If asked, enter your iPhone passcode.

Updating/upgrading your iPhone - Apple Community