My b2evolution Version: Not Entered

I have a few images that I've uploaded and which are surplus to requirements and are taking up space unnecessarily. When I try to delete them by hitting the delete icon in the attach images display, they don't disappear - well, OK, maybe that would just un-attach them, I don't know. In any case, it doesn't delete them. I want to remove them from the system entirely.

So I tried FTP, went to the folder and tried it - not permitted. Changed the permissions to 777 (also not permitted but the permissions seem to have changed anyway). Tried to delete - not permitted, still. Is there some command in the b2evolution interface that will delete them?