It's not clear from your question whether this is a self-published paper or a published paper. If it it is self-published paper, and you are the lead author (or project head), you can remove the co-author yourself, with notification to the wrongly-designated co-author. If this is a copyrighted, published paper, then you will need to direct your request to the publisher/editor of the publication and provide an explanation as to why you want the co-author removed. Good luck!