Featured Images HUGE, how to downsize them?

Hi!

I am using featured images and am having trouble with them because they are showing as HUGE on my website. http://thundergodroot.com/

I have scaled my images, figuring that would help, and it seems to make no difference what size the actual image is. The yellow hazard sign image that is so large is scaled to 300×300 I think, and its just gigantic on the page.

How can I fix this?

Thanks!