My header graphic image is not uploading?

The image that you are trying to upload should meet the following requirements:

For Classic:

• Recommended Width: 1280px
• Recommended Height: As per the aspect ratio.
• Maximum File Size: 5MB 
• Supported Formats: .jpg, .jpeg and .png

For Mosaic:

• Recommended Width: 1280px
• Recommended Height: As per the aspect ratio.
• Maximum File Size: 20MB 
• Supported Formats: .jpg, .jpeg and .png