You simply need to read the install documents and have a list of the plugins, if any, you've installed. All I would do is tell you the same things the documents say. It tells you what releases you can upgrade from. It is a pretty simple procedure. If you aren't used to doing system admin work find someone who is and have them help you. Just make sure you take a Jira backup and save a copy of the configuration file for reference.
In any case a common recommendation is to test on a non-production environment first.
The upgrade scenarios and detailed steps are documented here:
This documentation should get you started to plan and execute the upgrade.
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