First, see what your app looks like on iPhone 5. This can be done by including a Default-568h@2x.png
within your project. This is the launch image for iPhone 5, and indicates to the OS that you support the taller screen size.
If you've programmmed your application well (for example, with decent Autoresize masks), the OS should take care of most of it for you, and it'll look decent already. If you want to use AutoLayout in iOS 6, this will also help for the iPhone 5.
If it does not look that great, then you can do some conditional modifications for iPhone 5 using the macro:
#define IsTallPhone() ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPhone && [UIScreen mainScreen].bounds.size.height == 568)
So for example:
if (IsTallPhone()) {
frame = CGRectMake(0,0,200,500); // Use Tall Frame
}
else {
frame = CGRectMake(0,0,200,300); // Use Normal Frame
}
The conditional can be done for anything, for example to load a different .xib file. It entirely up to you.