Once you have created an app, submitted it to the App Store, it was then subsequently approved and you have now realized that you should have used a different name - unfortunately you cannot change the name of the app without resubmitting it to the App Store team for review. We had a similar problem and this is what we received from the good fellas at Apple (thank you Apple):
Application names can only be edited in scenarios where your newly set app name will be reviewed by Apple.
These application review channels are as follows:
1) You are uploading a new binary for your application
2) Your application has been rejected by Apple and is in the "Rejected" state in iTunes Connect (can be edited under Edit Information before replacing your binary)
3) You have rejected your own application and it is in the"Developer Rejected" state in iTunes Connect (can be edited under Edit Information before replacing your binary)
If you are unable to edit your application name, it is because you are attempting to change your app name outside of the permitted scenarios listed above.
Changing the application name via iTunes Connect will affect your application name as it displays on the App Store only.
The app name that you enter in iTunes Connect may slightly differ from the app name a user will see after installing your app on their device. This is because the app name that appears on a user's device is determined by the app name provided in your binary and not by the name that you provide in iTunes Connect. The name provided in iTunes Connect will display on the App Store. These two app names must be consistent and as closely similar as possible.
If you need to change the application name that is tied to your application icon when it is downloaded to a device, you will need to edit this name in the binary of your application and send a binary update.
Regarding the character limit for the app name as it appears on the device, we recommend that you use no more than 12 characters to prevent possible truncation.