I looked at my site

Hello, I looked at my site performance through gt metrix and I have an awful score in the serve scaled images... literally a 0. This entire time I thought it was an image optimization thing. So when I saw that it told me my images where being scaled down from ex. 500 x 500 to 299 x 299 I resized them and uploaded them..but then the image looked smaller. My question is how do I fix this? My wordpress site is responsive and Im not sure if that has anything to do with it. But I don't want it to kill my rankings, SEO, or load time. Please let me know what I can do?