Increase Logo Image Size to full width

I read on this forum how to increase the logo image size in the header, as our logo has text at the bottom that needed to appear larger on our website. When we did this, due to the shape of the logo, it created a lot of white empty space on the right side of the page. We would like to upload an image that is wider, with the logo on one side and a quote on the right to fill in this space. When I upload the new logo image, it only allows it to go to the halfway point and will cut the image off if we increase the height. How can we allow for a wide image the width of the site as our logo image?

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