Open the Google Photos app or go to photos.google.com
Sign in to the Google account that contains the backup photos
Select the photos you want to delete
Tap or click the Trash/Delete icon
Confirm the deletion
Open the Trash or Bin
Empty the Trash or Bin to permanently delete the photos
If you want to remove photos only from Google Photos and keep them on your device, turn off Backup before deleting
If photos are synced, delete them from Google Photos and then check your device storage settings if needed
On Android, open Google Photos, select photos, tap Delete, then empty Trash
On iPhone, open Google Photos, select photos, tap Delete, then empty Trash
On a computer, select photos in Google Photos, click Delete, then go to Trash and empty it