There is no easy way to do it from the GUI, as far as I know, but you do have the DeleteChildren
method on IContentRepository
. So creating a scheduled job or a plugin to do it for you should be pretty straightforward.
IContentRepository _contentRepository; // Get this from whereever
var blockRoot = new ContentReference(123); // Get this from whereever, i.e. a property on your startpage
_contentRepository.DeleteChildren(blockRoot, true, AccessLevel.NoAccess);
Also, if you do this on your media data, remember to run the "Remove abandoned BLOBs" scheduled job afterwards (unless it's autorunning on intervals) to clear up disk space.