At the iPhone launch, Apple announced that the release date for iOS 7.0 will be on September 18, 2013 (probably around 1 PM Eastern or 10 AM Pacific time). In the past Apple has released updates around 10:00 A.M. Pacific time. It will be available for iPhone 4, iPhone 4S and iPhone 5.
Make sure you have 3.1 GB of storage on your device or else you may not be able to update to iOS 7.0
Note: You may need to download iTunes 11.1 to get iOS 7.0 to sync: http://www.apple.com/itunes/download/