Unpublishing content is easy. To turn a piece of content back to a draft, start by:
Navigating to the content section that your piece of content belongs to, under the Publish menu
Once you've found the piece of content you want to unpublish, click Edit
Scroll down to the Publish section, and select Edit next to the 'Status: Published' field
Select Draft from the dropdown, and then select OK
Select the green Update button in the lower right hand corner - you're all set!