Dropbox Business will keep your deleted files and version history for 120 days (this may increase in the future). This means if you delete a file, you can recover it for up to 120 days. If you are actively working on a file, you can restore any version for up to 120 days.

If the file is not deleted, you can initiate the process from the desktop app or the web interface. From your computer, right click on the file and select Version History as shown below. This action will open your default web browser to access your Dropbox.com account. 

Just select the version you want to restore and click the Restore button as shown below. This will restore the selected version as the current version.