To upgrade pluggable databases (PDBs) that are in an earlier release multitenant container databases (CDBs), Oracle Database Release 12c (12.1.0.1) and later, you can unplug the PDBs from the earlier release CDB, and plug the PDBs into the later release CDB.

• About Upgrading Pluggable Databases (PDBs) Sequentially
  You can upgrade PDBs by unplugging a PDB from an earlier release CDB, plugging it into a later release CDB, and then upgrading that PDB to the later release.