Disabling thumbnails in posts

I’m using the Oxygen theme, which currently shows my posts on the homepage in excerpt form with a thumbnail for each post. I know how to convert the excerpt to content (in the index.php), but I cannot figure out how to remove the thumbnail. When I change the excerpt to content on the home page, the thumbnail is still there. I’d really appreciate any suggestions to fix this. I’ve searched the archives and haven’t found a solution to this specific problem. Thanks!