Why I can't upgrade my 5s to iOS 10.2.1

Hello,

Try these steps:

Remove and download the iOS update again

If you still can't install the latest version of iOS, try downloading the update again:

1. Go to Settings > General > Storage & iCloud Usage. Under Storage tap Manage Storage.
2. Find the iOS update in the list of apps.
3. Tap the iOS update, then tap Delete Update.
4. Go to Settings > General > Software Update and download the latest iOS update.

If you don’t see the update in the list of apps or if the issue happens again, you need to update your device with iTunes.

More troubleshooting steps here:

Get help with over-the-air iOS updates - Apple Support

Apple servers may be busy. When they say try again later... then try again later.

Make sure to backup your data prior to upgrading.

How to back up your iPhone, iPad, and iPod touch - Apple Support

Did you try to connect to iTunes on your computer and check for an update? You can choose to download it first and install it in a second step.

Hi

Try update again over your WiFi .

Cheers

Brian