Affiliate website. Problem with image sizing.

Hi Guys,

I am an absolute newbie and have built (attempted to) an affiliate store using Polaris theme and datafeedr.
The issue I have is that I have various merchants therefore their image dimensions differ. Some product images import great into the catalogue boxes and single product page but others wont fit, they are too large and are cropped or are blurry.

What I want to know is there a simple way to ensure that all images are scaled appropriately to fit in the containers and maintain their aspect ratio?

I have tried various things in woocommerce/ display settings and regenerated thumbnails but nothing appears to have changed.

I really have no idea what i’m doing and would be so grateful for some help, as this issue is preventing me from progressing my site.