A plain Bugzilla is fairly easy to upgrade from one version to a + newer one. Always read the release notes to see if there are any issues + that you might need to take note of. It is recommended that you take a + backup of your database and your entire Bugzilla installation before attempting an + upgrade. You can upgrade a 'clean' installation by untarring a new + tarball over the old installation. If you are upgrading from 2.12 or + later, and have cvs installed, you can type cvs -z3 update, + and resolve conflicts if there are any. +
However, things get a bit more complicated if you've made + changes to Bugzilla's code. In this case, you may have to re-make or + reapply those changes. One good method is to take a diff of your customised + version against the original, so you can survey all that you've changed. + Hopefully, templatisation will reduce the need for + this in the future.
From version 2.8 onwards, Bugzilla databases can be automatically + carried forward during an upgrade. However, because the developers of + Bugzilla are constantly adding new + tables, columns and fields, you'll probably get SQL errors if you just + update the code and attempt to use Bugzilla. Always run the + checksetup.pl + script whenever you upgrade your installation.
If you are running Bugzilla version 2.8 or lower, and wish to + upgrade to the latest version, please consult the file, + "UPGRADING-pre-2.8" in the Bugzilla root directory after untarring the + archive.