How to delete photos from iCloud?

See the article Delete and recover photos and videos on iCloud.com - Apple Support

Delete photos and videos

1. In Photos on iCloud.com, select the photos or videos you want to delete, or double-click a single photo or video.
2. Click , then click Delete.
3. Deleted photos and videos are moved to the Recently Deleted album.
4. To permanently delete photos or videos before they are automatically deleted, go to the Recently Deleted album, select the items you want to delete, then click Delete [number] Items.

See also Delete photos or videos from your Shared Library.