How can I upgrade my iPhone 7 Plus to iOS 15.7.3

Hello,

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

Please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information.