Once an app has been released, or if it's rejected during the review process, you can't make changes to the app until you create a new version of it.
If you create a new version of a released app, both versions of the app appear in the Developer Portal until the new version is released. When the new version is released, the previous version is no longer available.
If you create a new version of a rejected app, the new version of the app is displayed instead of the previous version and the previous version is no longer available.
An app can have, at most, two versions: the current version and the previous version.
To learn how to create a new app version, see Create a new app version.