You can't. The only version of iOS signed for the 4S right now (aside from the betas) is 7.0.6.I have an iPhone 4S running iOS 6.1.3. When I load it in iTunes, it tells me that iOS 7.0.6 is available. But I read that there's an iOS 6.1.6. How do I tell iTunes to install 6.1.6 instead of iOS 7.0.6?