If you would like to upgrade the database via CLI interface, you may refer to this post: How to Move 11.2.0.2 Database to 11.2.0.4 Environment and Upgrade
When we have already prepared the environment for the database to upgrade, then we can initiate DBUA.
[oracle@db11204 ~]$ dbua
[oracle@db11204 ~]$ dbua
Database upgrade has been completed successfully, and the database is ready to use.
The following document describes important behavioral changes from previous database releases:
/u01/app/oracle/product/11.2.0/dbhome_1/assistants/dbua/doc/DefaultBehaviorChanges.html