Greetings oona193,
Thank you for using Apple Support Communities. It seems like you are trying to update the iPhone, but it says this update can't be done. Since you are trying to update over Wi-Fi, try updating using a computer instead.
- "On a Mac with macOS Catalina 10.15, open Finder. On a Mac with macOS Mojave 10.14 or earlier, or on a PC, open iTunes.
- Connect your device to your computer.
- Locate your device on your computer.
- Click General or Settings, then click Check for Update.
- Click Download and Update.
- If asked, enter your passcode. If you don't know your passcode, learn what to do."
Update your iPhone, iPad, or iPod touch
Please don't hesitate to let us know if the steps resolved your issue or if you need additional assistance.
Take care.