Question

The white square meaning the background? 

2 ways:

1. Go back to the original bitmap and edit out the white background color in your favorite image editing program and save it as PNG-24 with alpha. Import back into AnCC
2. In AnCC select the bitmap with white background and use the Trace Bitmap feature to convert it to vector, select the white area and delete it. 

Personally, option 1 is your best choice since trace bitmap will likely change the overall look of your image and possibly create to many vectors to maintain its integrity.