Remove header from website

Hi - I am trying to remove the header from my website - from all of the pages. Please can you assist. I have copied an image of this below. I am trying to remove the area highlighted in red.

Thank you for your help.

Hey there,

I hope you are well today and thank you for your question.

You can try achieving this by adding the following CSS code in the Custom CSS option of your theme on the below path.

Admin Area -> Appearance -> Customize -> Additional CSS

/*remove nav menu*/
nav.navbar.navbar-default {
    display: none !important;
}

Best regards,
Support.