A bug from 2010 still active in latest version. Surely should be available in one of the menus! Not just swipe gesture (doesn't work).
April 23, 2008
left to right swiping is no longer standard for deleting rows in iOS7 and onwards - only right to left. That contextual menu is pretty long as it is, so we ask you to try to get used to swiping from right to left to delete files!
once more for the web crawlers out there: swipe from RIGHT to LEFT to delete files in DropCopy