Please how can I update my iPhone 7

You can update the iPhone 7 to the most recent release of iOS 15 – currently iOS 15.8.1.

About iOS 15 Updates - Apple Support

You cannot update the iPhone 7 Plus to iOS 16 or later.

To update to the most recent, compatible version, 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. 

iPhone 7 cannot update to iOS 16 or iOS 17, if that might be what you are looking for.