You can delete photos from My Photo Stream using iPhoto 9.2.2 or later, or any iOS device with iOS 5.1 or later.
When you delete a photo from My Photo Stream, the photo is removed from My Photo Stream in iPhoto and is automatically deleted from My Photo Stream on all other devices and computers that use the same iCloud account and have the required software.
Important: Any photo from My Photo Stream that was downloaded to your device while it was running iOS 5.0.1 or earlier must be deleted manually.
To add a deleted photo back to My Photo Stream, you need to upload the photo manually.
Select iCloud in the Source list and double-click My Photo Stream.
Do any of the following:
Select the photos you want to delete, and press the Delete key.
Select the photos you want to delete, and choose Photos > “Delete from My Photo Stream.”
Control-click the photos you want to delete, and choose “Delete from My Photo Stream” from the shortcut menu.
Drag the photos you want to delete to Trash in the Source list.
Photos that have already been imported from My Photo Stream into events in your iPhoto library aren’t deleted from those events.