If a collection is selected and opened in a tab, there are 3 variants to delete documents.
In all three available views of documents, there is a button or an icon to delete a single record. After clicking the button and confirming a security query the document is deleted and the view is updated.
In table view there is also the possibility to select the checkboxes next to each document or to select all records with the checkbox "Select All" in the table header. The button "Delete document(s)" will appear in the toolbar. After confirming the security query, the documents are deleted and the number of deleted items will be shown in a on-screen message.
Of course documents can also be deleted in console mode.
In console mode, there is no security confirmation prompt for deletion!
More about deleting documents in console mode can be found here http://docs.mongodb.org/manual/tutorial/remove-documents/