Changing size of thumbnails for one category

Hi,
My theme sets thumbnails as being horizontal and I would like to swap the dimensions from 330×220 to 220×320, but only in one category.
It currently looks like this: https://www.deborah-levy.com/category/books/
I would like 2 per row (though not main priority, would rather fix the thumbnail size), and
for them to be vertical rather than horizontal. Is there any way I can do this just for one category?
The theme i’m using is called SimpleMag.

Thank you!