How can I update my iPhone to the latest iOS version?

On what iPhone model? which iOS version is currently running on it?

After identifying your iPhone model, see this compatibility list:

Assuming your model supports the latest iOS version, these are the instructions:--> Update your iPhone, iPad, or iPod touch

Specifically:

Assuming you're trying to update your device wirelessly (Settings>General>Software Update), and bearing in mind that to perform such a procedure you need to connect your device to a reliable and fast Wifi Network with Internet access (no cellular data, unless you use a 5G network, no personal hotspot on your device, no VPN connections are admitted, no Low Power Mode enabled, and I suggest that you keep the device plugged into power during the whole update process), read this support article:--> If your iPhone, iPad or iPod touch won’t update (if you don't have a reliable and fast wifi network, "borrow" one from your relatives/friends/neighbors).

Also, make sure your device is NOT running a Beta operating system version. Should be this case, you need to remove it before installing any official iOS/iPadOS releases, as per these instructions:--> How to uninstall iOS or iPadOS beta software - Apple Support.

DO NOT forget to create a full backup of your device before updating its operating system, and keep in mind that, depending on the available storage on your device and/or on your wifi network speed, it might take 30-60 minutes to complete the entire update process.

If the issue persists or if the iOS version currently running on your device is very old, try to update it via computer (if you don't have a computer borrow one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service Provider), then learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.

If you still get no help, contact Apple Support directly, using this link:--> Contact Apple for support and service

Regards

Giulio

jimoh70 wrote:

I want to update my iPhone 7 iOS 13.5 to iOS 15.5

Since it is running the prehistoric iOS 13, you'll have many difficulties to update it wirelessly.

See the section (that I already posted in my first reply):

If the issue persists or if the iOS version currently running on your device is very old, try to update it via computer (if you don't have a computer borrow one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service Provider), then learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.

Regards

Giulio

Which iPhone model do you have and what version are you currently using?

You can update your iPhone to iOS 15.8.3 and that’s it. The hardware on your iPhone does not support iOS 16.X or higher.

Just run the updater at this path,

iPhone > Settings > General > Software Update

Go to Settings > General > Software Update. There is will tell you if any IOS updates are available.