I am unable to update iOS 17 on my iPhone 7

I am unable to update IOS 17 in my I phone 7

That is correct, you cannot update to iOS 17 with an iPhone 7.

You are also not able to update to iOS 16 with an iPhone 7.

So, your iPhone 7 is quite a bit out of date. You need a new phone to run newer iOS versions.

Ideally, you would want a phone that can run the new iOS 18. That would be an iPhone XR or higher model.

That's correct, if you own an iPhone 7. Just like you could not update that phone to iOS 16. iPhone 7 cannot be updated past iOS 15.8.3. It doesn't have the hardware required to support anything higher. If you need higher iOS versions, then you'll have to retire your very old, out of date iPhone and purchase a much newer, more modern iPhone.

You cannot pick and choose an iOS version. What you get is Settings > General > Software update > [All options are available here]

You need to correctly Identify your iPhone model - Apple Support

These are the iOS options based on an iPhone Model

(Dated: 22-MAR-2024 12:06:08 PM - GMT +05:30)

• iOS 17.6.1 —> iPhone models compatible with iOS 17 - Apple Support (IN)
  • A16 Bionic (4 nm) - 15 (6GB RAM) / 15 Plus (6GB RAM)
  • A17 Pro (3 nm) - 15 Pro (8GB RAM) / 15 Pro Max (8GB RAM)
  • Chipset A12 - XR (3GB RAM) / XS (4GB RAM)/ XS Max (4GB RAM)
  • Chipset A13 - SE (2020) (3GB RAM) / 11 (4GB RAM)/ 11 Pro (4GB RAM)/11 Pro Max (4GB RAM)
  • Chipset A14 - 12 Mini (4GB RAM) / 12 (4GB RAM) / 12 Pro (6GB RAM) / 12 Pro Max (6GB RAM)
  • Chipset A15 - SE (2022) (4GB RAM) / 13 Mini (4GB RAM) / 13 (4GB RAM) / 13 Pro (6GB RAM) / 13 Pro Max (6GB RAM)
  • Chipset A16 - 14 (6GB RAM)/ 14 Plus (6GB RAM) / 14 Pro (6GB RAM) / 14 Pro Max (6GB RAM)
• iOS 16.7.10 —> iOS 16 and iPadOS 16 are compatible with these devices
  • Chipset A11 - 8 (2GB RAM) / 8 Plus (3GB RAM) / X (3GB RAM)
• iOS 15.8.3 —> iOS 15 is compatible with these devices.
  • Chipset A9 - 6S (2GB RAM) / 6S Plus (2GB RAM) / SE (1st Gen) (2GB RAM)
  • Chipset A10 - 7 (2GB RAM) / 7 Plus (3GB RAM)
• iOS 12.5.7 —>
  • Chipset A7 - iPhone 5S (1GB RAM)
  • Chipset A8 - iPhone 6/6 Plus (1GB RAM)
• iOS 10.3.4 —>
  • Chipset A6 - iPhone 5 (1GB RAM)
• iOS 10.3.3 —>
  • Chipset A6 - iPhone 5C (1GB RAM)
• iOS 9.3.6 —> iPhone 4S (512MB RAM) - Chipset A5
• iOS 7.1.2 —> iPhone 4 (512MB RAM)- Chipset A4

Know how to...

• Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
• Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

Probbaly you are finding difficulty in using some apps which require iOS 17. --> Apps that require higher iOS versions than your device can be updated to... - Apple Community