I don't know where you are with your bitnami stack, but if you are on a linux system and can remove it with a package installer, that is where I would begin. A bitnami stack uses its own directory structure, its own php, its own apache, and security system and is, frankly, a pain. Then make sure you have apache and php installed in their normal places and that your old wiki still works from its usual url.
You could follow these instructions to upgrade:
https://www.dokuwiki.org/install:upgrade#upgrading_an_old_distribution
But, since your dokuwiki is so far out of date, this could be a lot of work, So, what I would do is this. First, retain your old copy of Dokuwiki; leave it in place, make no changes to it. Then download and unpack the latest dokuwiki. Then,
1. copy the old data directory to the new dokuwiki
2. now delete the files and directories in data/cache so that you are starting with a clean cache
3. do not delete the new new conf directory, but copy over all the files from your old conf directory to the new conf directory
4. copy your old plugins to the new plugins directory
5. change the owner of your plugins directory and your template directory to the web server. On Centos this is apache, on Ubuntu/Debian this is www-data. For instance:
chown -R www-data plugins
You might want to do this for the conf directory as well.
Now login as admin and go to the admin panel and open the Extensions Manager. Update all of your plugins, as required.
Now, there is the question of your template. If you have been using the standard Dokuwiki template, then there is nothing more to do, If not, from the Extensions Manager, check your template and if need be upgrade.
When you are happy with the result, rename your new dokuwiki to the old name, but don't delete the old, just so you have it in reserve as a backup.