How to upgrade my iPhone 4s?

I just ordered an iPhone 4s 8GB which comes with ios 5 or 6. If i try the upgrade option on the phone or iTunes it'll directly upgrade to iOS 8. I want to upgrade it to 7.1.2 but not iOS 8. How to do it? I saw from the website.apple is still signing the iOS 7.1.2 ipsw files for iPhone 4s.So i downloaded the iOS 7.1.2 ipsw file from apple website (around 1.21 GB) Is that even official and safe to restore that OS on my new iPhone 4s? And is there any other way?

I guess this article may help you, it tells the most common ios 8 update problems and solutions.http://www.imobie.com/support/common-ios-8-upgrade-problems-and-solutions.htm

If apple is still signing iOS 7.1.2 when you get your phone then you have to do it using this method.

1. Check if apple is still signing iOS 7.1.2 here: http://api.ineal.me/tss/status
2. Keep your.ipsw file
3. Update your iTunes
4. Shift + Left click on restore iphone and locate your ipsw.
5. Sit back and wait til iOS 7.1.2 is installed

Yes downloading from the apple site is completely safe

Hope this helps