Select the Revisions link/tab. You will see all previous revisions.
Create a Revision Log Message
Each type of content has a Create new revisions checkbox (defaults to being checked) and a Revision log message box.
A Revision log message is a short description of the changes you made to a content item. This message displays next to the revision when you review all revisions via the Revisions link/tab.
Image
Revert to a Previous Revision
In the Operations column, select Revert to revert to a previous revision or Delete to delete a revision.