My iPhone 6 wont show me the new update and it says it is up to date, I’m trying to install iOS 14

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)

That’s because iOS 12.4.8 is the most recent update that an iPhone 6 can install, AmberGasoline.

I’m sorry, but there is no update or upgrade that it can run, past that.

What you should do? You should buy a newer, current-gen iPhone. The iPhone 6 is too outdated / old and it's hardware cannot support iOS 13 or 14.

12.4.8 is the last version available for your device.