Delete photos and videos on iCloud.com
In Photos on iCloud.com, tap the Photos tab, then tap Select.
Tap the photos or videos you want to delete.
Tap the Delete button , then tap Delete.
You can also delete photos and videos from albums and folders.
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 iPhone before the 30-day time period is up. See Use iCloud Photos to store photos in iCloud in the Photos User Guide.