Every time a user edits a file using SharePoint, it creates a new version of that file. SharePoint saves all the versions of the file and allows you to roll back to any of the previous versions. For example, if there are 5 versions of a file and you decide to restore it to version 3, then SharePoint will create a new incremental version (version 6) identical to version 3 , and make that the current version.
Access the object that contains the file to be rolled back.
Click Attachments.
Click Expand to expand the folder that contains the attachment, if necessary.
Right-click the name of the file you wish to roll back and click Version History. or:
Right click on the file, click View Properties and click Previous Versions.
Click Restore next to the version you want to roll back to. A new incremental version is created and the file is restored to the selected version.
Note: A @ next to a version indicates that it is the current version of a file. Click Current Version to see additional details about the current version of a file.
(Optional) Click Current Version to see additional details about the current version of a file.
(Optional) Click File List to go back to the list of attachments linked to the object.