In iOS 6 Apple made it easy to convert your iPhone app to new 4-inch tall screen size. In XCode, select .xib or .storyboard file of your app, for example, MainWindow.xib or MainStoryboard_iPhone.storyboard, and go to File Inspector. Find “Use Autolayout” checkbox and check it. This will adjust all views according to screen size. Secondly, supply a larger default splash image of the new size 640 px by 1136 px and name it Default-568h@2x.png.

Within your app you can actually detect whether it is iPhone 5 or not and use the appropriate splash screen image. Use this code to detect iPhone 5:

#define IS_IPHONE_5 ( fabs( ( double )[ [ UIScreen mainScreen ] bounds ].size.height - ( double )568 ) < DBL_EPSILON ) 

and later in your app delegate

splashImage = (IS_IPHONE_5) ? @"Default-568h@2x.png" : @"Default.png"; 

The splash image will tell iOS what resolution you use. Possibly you need to adjust some fixed size views if any. But all my apps worked with new resolution correctly.