Update my iPhone to iOS 14

You likely have an iPhone 6 or earlier, and there are no updates past iOS 12.

iPhone 6 and earlier hardware is insufficient for iOS 13, iOS 14, and the current iOS 15.

There are no hardware upgrades.

If you need apps that require iOS 14 or iOS 15, your only options are an iPhone 6s or newer, or new.

Any recent i{hone will be substantially more capable than an iPhone 6, as well.

If you do have an iPhone 6s or newer, start here: Update your iPhone, iPad, or iPod touch - Apple Support