Your site uses very different-dimension images, so the images are cropped. If you want to use a custom image size on your site, you will need to make changes to the code.
Please find the following file in ColorMag: class-colormag-after-setup-theme.php. It is located inside colormag/inc/core/class-colormag-after-setup-theme.php. Move to Line 94 containing the following code: add_image_size( ‘colormag-featured-image-large’, 1400, 600, true );
Change the default size from 1400*600 to the one that suits you.
Once you change the image size, you must use the regenerate thumbnail plugin to regenerate images.
Also, more importantly, the size you change on your site can be overridden by the theme update, so we recommend you do such customization on your site using a child theme. For more details about the child theme, please check this link: https://themegrill.com/blog/tutorial-creating-wordpress-child-theme/