latest software update

What do you see when you go to Settings > General > Software Update > [Here?]

If you look at the screen, you'll see that your phone is ready to receive the update. You will get it right now, but the problem is that your phone is full, there isn't enough storage for you to be able to install it. You have a couple of options, one is you can go into the storage (using the storage button on that same screen) and clear out stuff that you don't need that is taking up a lot of data. The other is you can use a computer with the latest version of iTunes installed on it unless you have a Mac running Catalina (then you'll just have to use finder) and connect your phone to that and let the computer download and update the device for you. This will use the storage on your computer instead of your phone

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These are the iOS options based on iPhone Model --> Learn how to--> Update your iPhone, iPad, or iPod touch - Apple Support

• iOS 14.0.1 —> 6S / 6S Plus, SE (1st Gen and 2nd Gen), 7 / 7 Plus, 8 / 8 Plus, X, XR, XS /XS Max, 11,11 Pro /11 Pro Max
• iOS 12.4.8 —> Final release supported on iPhone 5S, iPhone 6/6 Plus, iPad Air, iPad Mini 2, iPad Mini 3 and iPod Touch (6th generation)
• iOS 10.3.4 —> Final release supported on iPhone 5 and iPad (4th generation) Wi-Fi + Cellular iOS 10.3.3 —> Final release supported on iPhone 5C and iPad (4th generation) Wi-Fi
• iOS 9.3.6 —> Final release supported on iPhone 4S, iPad 2 Wi-Fi + Cellular, iPad (3rd generation) Wi-Fi + Cellular, and iPad Mini (1st generation) Wi-Fi + Cellular
• iOS 9.3.5 —> Final release supported on iPod Touch (5th generation), iPad 2 Wi-Fi, iPad (3rd generation) Wi-Fi, and iPad Mini (1st generation) Wi-Fi
• iOS 7.1.2  —> Final release supported on iPhone 4.
• iOS 6.1.5 —> Final release supported on iPhone 3GS, and iPod Touch (4th generation)