The name can't be changed immediately. It must be confirmed by Apple and Google and must be unique - no other app with such a name in the stores. To change the name submit publishing of the new version of the app:
Go to Main Menu -> Apps -> Publish Mobile App -> Add New Version:
2. On the open page modify the app name and click the "Create and Send to Review" button:
3. Do it for both iOS and Android apps.
That's it. The update will take 2-4 days. We will let you know when the app is updated.