Hi ott814,
Thanks for using Apple Support Communities. From your post, I see you're unable to update your iPhone 4S to iOS 9.3.5.
There are some great steps here that you can use to
Get help with over-the-air iOS updates
:
If you try to update the iOS on your device, you might see one of these messages:

"Unable to Check for Update. An error occurred while checking for a software update."

"Unable to Verify Update. iOS failed verification because you are no longer connected to the Internet."
Try updating your device again using the same network. If you still see one of these messages, try updating your device using another network or update your device with iTunes. If the issue happens again after trying to update with multiple networks, remove the update.
If you still can't install the latest version of iOS, try downloading the update again:
- Go to Settings > General > [Device name] Storage.
- Find the iOS update in the list of apps.
- Tap the iOS update, then tap Delete Update.
- Go to Settings > General > Software Update and download the latest iOS update.
If you find the issue persists after you try the steps above, you may need to update using iTunes. Here's how to
Update your iPhone, iPad, or iPod touch
:
If you can’t update wirelessly on your iOS device, you can update manually using iTunes on a computer that you trust. If your computer is using Personal Hotspot on the iOS device that you’re updating, connect your computer to a different Wi-Fi or Ethernet network before you update.
- Install the latest version of iTunes on your computer.
- Connect your device to your computer.
- Open iTunes and select your device.
- Click Summary, 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.
I hope these steps help.
Have a great day.