In addition to this document, Oracle provides information about upgrades on its support site, and through its Pre-Upgrade Information Tool.
Through its support website, Oracle provides late-breaking updates, discussions, and best practices about pre-upgrade requirements, upgrade processes, post-upgrade, compatibility, and interoperability.
Oracle also strongly recommends that you download and run the Pre-Upgrade Information Tool, which is available on My Oracle Support.
My Oracle Support:
You can search in the library, or search on My Oracle Support for keywords, such as "Database Upgrade"
Oracle Database Pre-Upgrade Utility (Document ID 884522.1) at My Oracle Support