Adding a New Version to a managed Object Model
Add a new version to your managed object model when you need to change the schema in an application you have already released.
In the project navigator, select the managed object model.
Choose Editor > Add Model Version.
In the dialog, enter a name for the version, and select the previous version that it is based on.
To convert existing persistent stores to the new schema, use Core Data’s migration feature; see the definitive discussion for information on migration.
Core Data ignores the name of the model, so you can use your own naming scheme to keep track of revision numbers.
If you are using a source version control system such as Subversion, ensure that the new model version file is added to your repository.