Want excerpts to show full size first image instead of excerpts

I have excerpts for posts enabled on my home however I want the full size first image to be displayed and not the thumbnail. How can I do this? I figured out how to show the full size first image by adding the tag in ATO Don't strip this section under configure excerpts but when i do that the post thumbnail and the first image are displayed.

Thanks in advance for anyone's help on this.