Increasing header heighth for larger logo

I’m not sure if anybody’s able to help, but I’m setting up my blog with a new theme and can’t seem to increase the size of the header area to allow for my logo (without it overlapping into the navigation). You can see it at

I can shrink the logo but then you can’t read it. Not seeing anything that’s obvious in the stylesheet or the header.php (but I’m a little bit new to web development)

Thanks for any help…