How to update iPhone 7 to iOS 15.1?

You can update an iPhone 7 to the latest release of iOS 15. You cannot update it to a specific intermediate version like iOS 15.1.

Update your iPhone or iPad - Apple Support

"How to update iPhone 7 to iOS 15.1?: How do I update IOS 15.1 on iPhone 7"

-------

Updating an iPhone 7 to iOS15.1:

You Can't: Only the latest-compatible update would install: iOS 15.8.3. That's just the way Apple has it. So, update with a computer, and it will install sure enough: Update your iPhone Using a Computer - User Tip

iOS 15.1 is no longer available. iOS 15.8.3 is the current version for an iPhone 7.

Make sure that your iPhone 7 is setup to meet the following requirements before you attempt to update the iOS version over a Wi-Fi Network. Open Settings ➡️ General ➡️ Software Update: If there is an update available for your iPhone then it will be listed here. Follow the on-screen instructions to download and update your iPhone. 

• Your iPhone must have a fast Wi-Fi connection. You cannot update over a cellular hotspot
• The iPhone can not be in Low Power mode
• The battery state of charge must be above 50%
• Your iPhone must have at least 15GB or more free storage space
• Your iPhone cannot be connected through VPN
• You should leave the phone plugged in until it finishes updating, both to assure that it remains above 50% and to keep Wi-Fi enabled (Wi-Fi turns off when the phone sleeps if not connected to power)

Axel F.