Header banner

Try this in your custom css:

#header {height:180px; background-image:url('https://mha.gov.bd/wp-content/uploads/2015/05/New-Heder-up-1040x220.jpg')}
#header .logo {display:none}
.menu-secondary-container {margin-top:0}

Replace the image url with a url to your own image.

If your theme does not have a setting where you can enter custom css, you can use a plugin like this one:
https://www.ads-software.com/plugins/simple-custom-css/

Thank you so much @lorro. It’s working. How can we make it responsive img?

Your site is not available from here. Some kind of DNS error. It was working fine yesterday.