When one attaches a file to a forum post, there is a way to replace (by attaching another file), but there is no way to delete it (unless one goes into the moodle data directory - ordinary users can't do this of course).

We are currently doing an some activities where learners need to attach files to forum posts, but sometimes they do it on the wrong post. It would be great is a feature could that added that would allow the file to be deleted.