Return Value of CustomPress Upload Field


I'm using upload field of CustomPress. When I tried to echo the shortcode by using echo do_shortcode('[ct id="some_code_here" property="value"]'), instead of one img tag, I got 4 img tags. My best guess is these are actually thumbnail, medium, large and original version of the uploaded images. So my question is how to get the specified version of the image?

Another question is I can only upload and replace the file of the custom field, but can't delete the uploaded file, or reset the field. Is there a way to do this?