You can delete documents individually by:
iPad: swiping from right to left over the document in the list. You should then see a red "Delete" displayed.
Android: tap and hold the document name and a popup will be displayed to delete the document. Then select "Delete".
To delete multiple documents at one time:
Both devices: Click on the "Edit" on the document list page. You can then select documents individually or you can select either all documents or all submitted documents by hitting the "Select".