You don't even need to upgrade. Just go to your workspace settings and look for the export/import tab. I personally put the downloaded zip file through https:/

You don't even need to upgrade. Just go to your workspace settings and look for the export/import tab. I personally put the downloaded zip file through https://github.com/akkartik/slack-archive https://github.com/akkartik/slack-archive. But there are a variety of tools that can read the zip file.