Header image resizing (Arras theme)

The themes website is here: https://www.arrastheme.com/
My website: https://www.animevision.tv

Basically, the header image is being resized, no matter how big i upload it, it always ends up being smaller than it should.

I’ve tried the following:

Altering the header.php file so that it is an image code instead of the PHP, putting the image outside of all of the div tags etc.

I’ve tried altering the CSS files so that the logo area is bigger, and so that the header area is bigger. The header area (#branding) does change but the image size does not.
I’ve also tried adding new code to the CSS files. does nothing.

I’ve tried installing Dynamic headers plugin, which is what is currently in use at the moment but this hasn’t worked.

After that I decided to try uploading the image to the media and altering the size there, the size is correct on the scaling but soon as I click the image it is smaller than it should be.

I’ve checked the media settings and all of the settings are larger than the image, except for the thumbnails which is smaller than the resized image.

So I’m basically thinking this is something to do with the attachments or the javascript the theme uses?
The images for dynamic header are uploaded in a different folder to all the attachment images so It seems as if whatever setting is effecting the header is effecting all of them.

The only changes to the theme I have made, have been to change the width of the content area and the slider.

I have tried to google this issue as well as checking the arras forum (and posting there) but It just seems to be a ton of responses about changing the header area background, but that isn’t really a resolution :/

Any help is much appreciated.