Is there a way to select the featured side image size in Supermag theme?

I upload pictures with larger resolution as part of the content on the side, and I run the featured section on the main page. That results in the main page having a long loading time.

Is there a way to select the 240*172 picture instead of the full size picture, so I can reduce the loading time? Because website automaticly converts the 6000×4000 to 240×172 anyway, each time that I upload the picture.