How to update iPhone

How far you can update an iPhone depends on its model.

For instance, the iPhone 5s, 6, and 6 Plus cannot run anything higher than the latest release of iOS 12. You won't be offered updates to iOS 13 (or higher) for those phones.

If there are further updates for your iPhone, and you are having trouble figuring out how to install them, see:

Update your iPhone or iPad - Apple Support

Updating iOS: common issues and solutions - Apple Community