-Click on the image you want for your Facebook cover Photo.
-Save this image (right click on it and 'Save image/target as')
To add a cover photo to your timeline:
- Go to your timeline
- Click Add a Cover
- Choose whether you want to upload a new photo or pick a photo from one of your existing photo albums
- Once you choose a photo, you can reposition it by clicking on the image and dragging it up or down
- Click Save