The migration process involves run-time migration (moving your applications to a new run-time) and compiler migration (compiling your source programs with the new compiler). As part of the migration process, you'll also need to do inventory assessment and testing. As stated previously, you are not required to migrate your run-time and source concurrently.
For more details on the migration process, see General conversion tasks.
For information on performing an inventory assessment and test plan, see Take an inventory of your applications.