How to update my iPhone iOS?

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. 

1. Open the Settings app on your iOS device.

2. Tap General.

3. Tap Software Update.

4. Tap Download and Install, if an update is available.

5. Follow the onscreen instructions to complete the installation.

6. Your iOS device should now be up to date.

The maximum version of iOS available for the following Apple devices is:

- iPhone 3: iOS 7.1.2

- iPhone 4: iOS 7.1.2

- iPhone 5 / 5C: iOS 10.3.4

- iPhone 5S: iOS 12.4.5

- iPhone 6 / 6S: iOS 13.5.1

- iPhone 6 Plus / 6S Plus: iOS 13.5.1

- iPhone SE (1st generation): iOS 13.5.1

- iPhone 7 and 7 Plus: iOS 14.3

- iPhone 8 and 8 Plus: iOS 14.3

- iPhone X, XS, and XS Max: iOS 14.3

- iPhone XR: iOS 14.3

- iPhone 11, 11 Pro, and 11 Pro Max: iOS 14.3

,zzane

zzane wrote:

…

- iPhone 3: iOS 7.1.2

- iPhone 4: iOS 7.1.2

- iPhone 5 / 5C: iOS 10.3.4

- iPhone 5S: iOS 12.4.5

- iPhone 6 / 6S: iOS 13.5.1

- iPhone 6 Plus / 6S Plus: iOS 13.5.1

- iPhone SE (1st generation): iOS 13.5.1

- iPhone 7 and 7 Plus: iOS 14.3

- iPhone 8 and 8 Plus: iOS 14.3

- iPhone X, XS, and XS Max: iOS 14.3

- iPhone XR: iOS 14.3

- iPhone 11, 11 Pro, and 11 Pro Max: iOS 14.3

Parts of that list are incorrect. (Stale?)

Some of the errors, off the top…

iPhone 5S is limited to iOS 12, currently 12.5.7.

iPhone 6 is limited to iOS 12, currently 12.5.7. It cannot get to iOS 13 or later.

iPhone 6S and iPhone 7 are limited to iOS 15.

iPhone 8 and iPhone X are limited to iOS 16.

iPhone XR, XS, and later can run iOS 17.