How to change the size of the Youtube video in the sidebar?

Hi-

I've installed the Youtube Featured video, and it seems great, except that the video is showing up as too big for the sidebar! (see for example http://gatherwell.com/what-sunfunder-teaches-us-about-crowdfunding-for-a-green-cause/)

How can I change the size?

Thanks and Be Well,
Cynthia