How to upgrade iPhone 4S to iOS 7 instead of iOS 8 or 9?

I currently have iOS 6 on my phone.
From iTunes, I can go directly to iOS 9.
From Settings > General > Software Update, I can go to iOS 8.

I don't want these 2 iOS versions but iOS 7 instead. How can I upgrade to iOS 7 only?

Added (1). But I can still upgrade to iOS 8 right?

Not possible.

Apple "signs" the iOS versions that can and can't be installed on an iPhone model. This is usually the latest version that's compatible with that iPhone.
The latest iPhone 4s iOS version is iOS 9.1, which means that you have to update to iOS 9.

There's absolutely no way to ever install an unsigned iOS firmware anymore on newer iOS devices. Your'e too late at this point.

IOS 9 runs great. I like the background app refresh feature. Apps remain open hours after using them without having to reload yay!