paint.net - Delete background of an image and add it without background -

how can delete background of image , add layer without background? can far delete background, when add image on background deleted program treats though there background. stuck. here image before deleting background:

here image after deleted background on it:

here when try add picture without background picture:

as can see picture without background still has background goes on other pictures. tried use magic wand selected rectangle image, selects entire layer.