1. Click the Settings button
2. Click Direct Fulfillment Settings
3. Change the Customer Crop radio button to No
4. Don't forget to click the Save button at the bottom of the page.

Also keep in mind that with the native aspect ratio, a lot of print sizes will not retain the 3:2 aspect ratio (e.g. a 4x6" will, but a 5x7" is a different aspect ratio). By turning the feature off, you will need to ensure that the image aspect ratio matches the print size sold. If they're all in keeping though, you wont have to do anything differently. Here's a good little article that illustrates the problem facing every photographer: http://www.digital-slr-guide.com/aspect-ratio.html