Documentation for JIRA 4.3. Documentation for other versions of JIRA is available too. 
The procedure for upgrading JIRA changes little from one JIRA version to the next. However, each major release of JIRA comes with specific recommendations for upgrading from the previous major version.
If you plan to skip a few JIRA versions for your next JIRA upgrade, then we strongly recommend reading the upgrade guides for all major versions between your current version and the version to which you are upgrading. These version-specific upgrade guides contain important information that may be relevant to your JIRA installation.
For example:
If you plan to upgrade from JIRA 4.0 to JIRA 4.3, then read the upgrade guides for JIRA 4.1 and JIRA 4.2, as well as those for JIRA 4.3.
We also recommend that you read the upgrade guides for any minor releases listed below, since these guides contain important information that may be relevant to your JIRA upgrade.
Below is a list of upgrade guides for all previous major and minor releases of JIRA, each of which has important upgrade information: You will find the upgrade notes attached to the release notes for the relevant version.
Upgrade guides for minor releases are indented.
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