Hello mate you could use custom CSS.

Not too up on CSS. However, I can make minor changes. Can you provide a sample and then I can adjust?

You want to first add custom CSS to control the width of the email capture form. By default the max width is 640px. So you could do:

.somdn-capture-email-wrap-form,
.somdn-capture-email-wrap-form-wrap {
	width: 850px;
}

And then the width of the image container could be changed as well. By default it's 40% of the total width. So you could do:

.somdn-capture-email-left {
	width: 55%;
}

Now the image itself is set to be no bigger than 200px. So you could change that as well:

.somdn-capture-email-image {
	width: 400px;
}

You could put anything you want there really because the image is responsive and won't ever go outside the container. Have a play around using Chrome Developer tools.

Didn't do anything to change the image size in the popup. It's still cut off at the top and bottom. The size uploaded is 300x250. I added the CSS in the theme's additional CSS field.

Post a link to the product and I'll take a look.

Here is the link and notice the popup image: https://oilmanmagazine.com/product/oil-and-gas-museums/

Ah I see. That's because the plugin grabs the default thumbnail size for the image, which on your site is 240x172px, as seen below.

I plan on adding the option to choose which sized image you want to display but haven't gotten round to it yet.