How to update my iPhone 7?

The iPhone 7 can update until iOS 15.8

to update, go to settings>general>software update and make sure to turn off low power mode and connect to a wifi network

If updating wirelessly is not working 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 On the iPhone 15 series, use an usb c 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. On the iPhone 15 series, use an usb c 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.

See this user tip about updating that I've written for further reference

Updating/upgrading your iPhone - Apple Community

Hello,

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

Your iPhone 7 will currently only update to iOS 15.8

This support article has instructions about updating an iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support Read the article for recommended criteria for being able to use wireless updating.

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

If you want a video about doing this, follow this link —> https://www.youtube.com/watch/1FcE86kwODQ

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. If you want to run a higher system version than your current device is capable of running, you need to buy a newer device.

Please See: How can I update my iPhone please? - Apple Community