Delete photos and videos on iCloud.com
In Photos on iCloud.com, open an album or folder to select the photos or videos you want to delete, or double-click a single photo or video.
Click the Delete button , then click Delete.
Deleted photos and videos are placed in the Recently Deleted album, where they remain for 30 days. After that, items are permanently removed from all your devices set up for iCloud Photos.
You can remove items from your Mac before the 30-day time period is up. See Use iCloud Photos to store photos in iCloud in the Photos User Guide.