When using DSM Free, your library exists as a working draft that will update automatically any time you make a change. This draft is available to all collaborators you’ve invited to your library.
There is no way to roll back to a previous version of a library on DSM Free.
With DSM Enterprise, you have access to version control. This allows you to work in a draft until you’re ready to publish. After you’ve published, you can always revert to a previously published version. When you do so, the draft updates to reflect the previous version you selected.
If you revert to a previous version, it will overwrite the draft. If you don't want to lose any changes made to the draft, publish your changes before reverting to a previous version.