To upgrade an earlier TWiki version like 01 Sep 1999 to version 01 May 2000 you should do the following things:
Back up your system.
Update the templates in the /templates directory (and its subdirs):
Take the templates of the latest distribution as the base and merge your changes back into it.
Update the Perl scripts in the /bin directory:
Take the scripts of the latest distribution as the base and merge your changes back into it. Do so also for wikicfg.pm because it has important changes as well.
Update topics:
Copy the new Main. TWikiPreferences topic (and *,v file) into your TWiki.Main web. Customize the topic to your needs.
In case you are on an Intranet: Copy topic TWikiRegistration to Main.TWikiRegistration. Customize if needed.
In case you are on a public server: Copy topic TWikiRegistrationPub to Main.TWikiRegistration. Customize if needed.
Copy the Main. TWikiWebsTable topic (and *,v file) into your Main web and customize it. Reason: The new release does not use the *.inc include files anymore.
Optionally: Search for %INCLUDE%'s in all your webs and change them to the new %INCLUDE{"file.ext"}% syntax. Note: Your old %INCLUDE:"file.ext"% syntax still works (the legacy rule is defined in wikicfg.pm .)