When updating from previously installed versions this document points out obvious "gotchas" or other known implications. Of course it is often difficult to anticipate all potential interactions with localized installations.The procedure [INSTALL]UPDATE_CLEANUP.COM attempts to clean up any files known to exist in previous versions and that are no longer required. Execute it after an update.
Be sure to read about significant changes (although this is not exhaustive), and the revised Technical Overview and to a lesser extent the Environment Overview.
8.3 to 8.4
8.2 to 8.3
8.1 to 8.2
8.0 to 8.1
$ SET DEFAULT SYS$SYSTEM $ MCR AUTHORIZE UAF> ADD /PROXY 0::HTTP$SERVER HTTP$NOBODY /DEFAULT
7.2 to 8.0
7.1 to 7.2
7.0 to 7.1
6.n to 7.0
6.0 to 6.1
5.n to 6.0
5.2 to 5.3
5.1 to 5.2
5.0 to 5.1
4.n to 5.0
4.4 to 4.5
4.n to 4.4
3.n to 4.n