Reply To: Change Size of Image

@train4yourself: Hello there,
To change the Header Image
Go to => Appearance => Customize => Header Media => Add New Image and Publish.

To change the height of the image
Go to => Appearance => Customize => Additional CSS =>and add the following CSS Code.

.home .custom-header {
    min-height: 50vh !important;
}

You can change the value of min-height according to your requirement.
Let me know if this works out!
Kind Regards,
Skandha