Enlarging Featured Image on posts

Hello, I have a simple and quick question. I’ve added in a featured image into a post, but the theme I am using, “Athena”, will not show the entirety, or most, of the image upon loading the page.
Is there a way to move the Title of the page further down with a spacer for example, in order to let the featured image become less restricted?
Or is there another way to enlarge the image?

I am completely new to WordPress, which may be why I have this problem.

Thanks in advance.