Where to set the picture ratio of the homepage article

The theme is great, but after I installed it, I found that the proportion of the picture is not the same as the proportion of the picture on the demo. Can you tell me where to set the picture ratio of the homepage article？ Thanks！ https://s2.ax1x.com/2020/02/12/17aCrV.png [url=https://imgchr.com/i/17aCrV][img]https://s2.ax1x.com/2020/02/12/17aCrV.png[/img][/url] [](https://imgchr.com/i/17aCrV)