YouTube Thumbnails MaxRes

I would like my thumbnails for YouTube to use the MaxResdefault thumbnails always. But my site uses sd. Where in the php or css can I change this so that it always uses MaxRes? Is there a Plugin that can take care of this if I need to?

https://www.baselinedental.com is my site. The main YouTube Thumbnail I want shown is https://i.ytimg.com/vi/QJtFwbKn-C4/maxresdefault.jpg and not https://i.ytimg.com/vi/QJtFwbKn-C4/sddefault.jpg

Thanks