How can I delete a file from iCloud?

Can anybody tell me how I can delete a file from my iCloud account? I uploaded a few photos from iPhoto recently and have since edited the originals on my Mac, and want to update my iCloud backup with the amended files.

If you try and delete the duplicates that show up in iPhoto (under Photo Stream) it won't let you - it just asks you if you want to look for it. Most irritating.

It looks like once you upload a file to your iCloud account you cannot get at it. Surely that can't be how it's meant to be.

Bruce 😕