Within Teamwork Desk, you can see previous versions of each article, by clicking the revisions tab.
Revisions allow you to see each change that has been made to a doc, from the very first change right up to the most recent.
The revision tab can be found on existing articles you are editing:
You can then see a list of previous versions which include the date they were revised and which version is currently active:
To the right of the page you will see who made the revision and there is an option to view previous versions.
When viewing a previous version you can choose to make that the current one by selecting 'Restore':
For more information see: Changing the appearance of you Help Doc site