Please follow these following steps to Setup header image.
- Go to admin menu >> appearance >> customizer
- Go to header image >> add new image
- Select image either from Media library or Upload new image and insert it.
- Predefined crop size is available to crop the selected image so that your selected image will be of same size as shown in Demo. Please do crop the image of your size and press “Crop image”. You can change the crop size as well of your requirement.