Modify the size of the featured image

Hello, I need to adapt the sizes of the featured image to a different size.

I have two problems:

1. The featured image does not adapt.

My images are 1920×1080 and the formula of the template is different.

I have verified that it is given the size of 1080×820 with the class=”attachment-gutenix-thumb-post size-gutenix-thumb-post wp-post-image”.

2. The cover images of the blog page. I should be able to adapt them from the size of 1920×1080. I see that scale to 720×520

I don’t know what would be the best formula to be able to correct both aspects. I know that perhaps a formula would be to be able to use images in other sizes, but I already have a website with more than 3,000 articles, which is the one I am trying to export to your template, with more than 2,000 images at 1920×1080.

Thank′s for all.

The page I need help with: [log in to see the link]