Ok, just sharing, I figured out how to allow a larger image for my header.
To use any image size for header image you should slightly edit theme code. Inside custom-header.php file that you can find in Dazzling folder >> inc. You should add
flex-width’ => true,
right below this line:
flex-height’ => true,
Flex height was already in the custom header. php section.
After I added in the flex-width, I then went to appearance>header and reapplied my larger image. I did not hit crop image. The larger image appeared on my welcome page.
However, I need to figure out how to increase top margin above the image (using Jetpack)