Insert Header Image

[ Moderator note: moved to Fixing WordPress. ]

Greetings,

I just started using the ‘Oner’ theme. I’d like to replace the header background image area with an image that is larger than the space allowed. Is there any kind of custom code that I could use to override the default settings and use a larger image? Any help is appreciated. My site is currently displaying a “coming soon” page, so just let me know if I need to turn that off for you to help. Thanks!

Regards,
Luke