Desktop Workflow:
Start the workflow for the product you want and select the image to be used.
Once you are in the workflow and an image has been selected for the product, you can select the Photo Edits tab on the left, select the photo on the right and you should see the edits available for Brightness, Contrast, Full Color, Sepia and Black & White.
Mobile Workflow:
Start the workflow for the product you want and select the image to be used.
Once you are in the workflow and an image has been selected for the product, you can tap the image, then tap the photo edits button. Select the dropdown menu that shows brightness and select Brightness, Contrast, Tint, Sepia, Black & White or Full Color. Then select the Apply button for any options chosen.