You can customize the theme as per your requirement by creating a child theme. You can find detailed documentation to create a child theme here
After creating a child theme please paste the below-mentioned code in the child theme’s functions.php file.
* Enable support for custom logo.
add_theme_support( 'custom-logo', array(
'height' => YOUR_LOGO_HEIGHT,
'width' => YOUR_LOGO_WIDTH,
add_action( 'after_setup_theme', 'ecommerce_gem_setup_cust_logo',20 );
Logo with the bigger size might affect the look of your website menu that’s the reason we have given the fixed size for the logo.