Coraline Theme: Changing height of Featured Image

I’ve tried searching for ways in which I can change the max-height of the featured images on my website.

I found this code in functions.php: https://pastebin.com/PfmvE3ZT

I want the height of the image on the homepage to be bigger in height compared to the rest of the header images on other pages.

I thought that if I added: max-height: 418px; underneath max-width: 990px; this would enable the larger featured image on the homepage to display fully and not get cropped as it at the moment.

Does anyone know how to fix to this? Am I thinking along the right lines by adding a max-height value?

Thanks in advance for any help ??