Image sizes settings allow to change the size of the images used in different layouts. Although by default we are using the most common and recommended sizes for the most use cases, sometimes you may need to change some sizes. Int this case you must check these options and read the Option’s name and hints and find the option that will work for images you are interested in.

And if WooCommerce is installed, then it has its own image size settings:

If these options are changed, make sure to regenerate the thumbnails to update the existing images size.