You can resize your photo to the right dimensions for Facebook cover photos in Shutterstock Editor:
1. Click Create New on this page.
2. Choose Facebook Cover as your Canvas size.
3. Log in or create a free Shutterstock account if asked.
4. Add your image to Shutterstock Editor: File -> Upload images…
5. Choose your uploaded image and reposition it if needed.
6. Download the resized cover photo and use it on Facebook.