Although not clear from the documentation, it appears that you should unzip the new version on top of the existing version and allow the unzip process to overwrite any existing files.
You can then run public/upgrade and public/upgrade/complete_migration.php.
You then need to edit the config file and change 'og_' to 'fo_'
This transferred all of my setting and users, but did NOT transfer any of my documents, which are the most important part.
In the previous version my documents were saved as files, and they are still in the directory. What do I need to do to transfer them to V2?