On BitComet, as I remember, there is some option. When you delete torrent, it's still wvailable on archive, so, you can redownload it if you like.
If you need it in Qbittorrent, you need stop seeding or downloading, go to torrent folder, go to previous folder level, press shift-delete, confirm it. Please, make some archive, at lest option to delete data
If you add option sequential download, it allows download movies more easy.