Thumbail resolution

Hello everyone!

I’m using the EVC Post Carousel for news on our website.
Due to different sizes of the post images, I have set up “thumbnail” as image proportion.
The problem is that the thumbnail resolution is very low. Is it possible by any chance to increase the resolution of the thumbnail images?
Or else, are there other ways to select the section of the image to be displayed in the post carousel? If I would select image proportion “medium” for example, all images would have different proportion due to the different format of the original pictures. Also, they would not be square, as our theme uses wide picture.

Thanks in advance for all support!