Download "free" iOS 7 Apps to iPhone 5s

I bought an iPhone 5s in October and so should be able to download the following iOS 7 apps for free:

http://support.apple.com/kb/HT5913

• iPhoto
• iMovie
• Pages
• Numbers
• Keynote

However, when I try to download them from the App Store on my iPhone 5s, it give me a "buy" button, not a "free" button.

How do I get these apps for free?

Thank you for reading.

- nello