Making a Photo a Primary
Any photo in your album with a Make Primary link has already been approved to be used as your Primary Photo. Just click that link to make it your profile picture.
Don't see the Make Primary Link? All photos are reviewed before they are approved as a main, or album photo. If a photo meets the Primary Photo Requirements but is approved as Album Only, delete, and then re-upload the photo. This will ensure that it's re-reviewed, and if eligible you should see the Make Primary link after it is approved.