Height of images for cardinal theme

Im new here. Ive installed cardinal theme for wordpress and its fantastic.
I would like to change the size of images (for exemple max-width:100% by max-height:100% ) because I can’t see my full images on small screens like tablets.
Here is a portfolio item : http://www.clairechauvel.fr/painting/pres-de-ceyzerieu-huile-toile-diptyque-162x116cm-2016/

If anyone can help me I would be very gratefull !