Could you please this section of our documentation that explains how to upgrade Redmine?
Please note that you'll migrate from a really old version of the application, so I don't know if the commands to migrate the database will work or not, you'll probably need to run more commands. I suggest you ask in the official forums of the application in order to get more information about this migration, as I mentioned, it's a big upgrade.
Please, use the Bitnami environment when launching the commands
You'll also find a file called "use_redmine" in the installation directory.