I want to update my iPhone

Here are two different ways to ensure the highest iOS that your device will support is installed on your device.

For instructions about updating your iPhone, iPad, or iPod touch wirelessly, click here --> Update your iPhone or iPad - Apple Support

Here are instructions about how to update your iPhone, iPad, or iPod touch with the Finder on a Mac computer --> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Your device will update to the highest version currently available that it will support. Only iOS 12.5.7 is currently available for an iPhone 6 Plus