bittorrent - How to make a torrent from another torrent.?

Most of the torrent out there consist of various files or dir under it. Many times it happens that I want a single file or want to share a single file from it rather than sharing all of them. I want to know; suppose a torrent file having x, y, and z content files under it,. i want to share only file x. How can I make a sub-torrent from a torrent WITHOUT DOWNLOADING IT???... For a practical ex, there are various sites that allows direct download links. I want just one file from the torrent to download, but I cant even process it as its over a gb. However the file is under 1 GB. I hope someone can give an answer or show a direction. Anything related to content is welcomed. Sorry for my bad english.

In order to create a new torrent by keeping only some files, follow these steps:

1. Download BEncode Editor.
2. Make a backup of the original .torrent file.
3. Open the file using BEncode Editor, and expand the info node.
4. Remove all items items in the files subnode, except those you want to preserve.
5. Save the new torrent.

Note When editing .torrent files, any changes to the info structure will change the the torrent hash. This means you won't be able to download or upload files from/to peers having the original torrent.