Navigate to your Dashboard from the options at the top of the page.
Look in the "Projects" box on the left side and switch to the "Project Drafts" tab. Double-click the draft from the list that you'd like to delete.
This will bring you to a new page displaying the details of the draft. Just below the top white box, you'll see a yellow button (labeled "Continue Posting") and a delete icon that looks like an orange trashcan. Click the trashcan to delete the draft.