Revision Status Bar
The revision bar is located under your webmaster tabs and right above your content, while in view mode (specifically, View published). Click to quickly unpublish this revision.
This is an example of a status bar, with this content's most recent revision in published mode (no existing draft).
This is an example of a status bar for content with a published version, with a most recent draft revision. By unpublishing, the published version will become the most recent draft revision, overriding the existing draft.
Moderate tab
The Moderate tab is located above your content and reveals a list of revisions applied to that particular content item. A published revision shows up green in the list, while the draft revision shows up red. Click to quickly unpublish the published revision.
This is an example of a published revision taken from the revisions list (no existing draft).
Here is an example of revisions for content with a published version, but a most recent draft revision. By unpublishing this content, the published version will become the most recent draft revision, overriding the existing draft.