How to get header logo bigger

You can get logo enlarged by adding extra css to override max-height for logo set in this theme. Please check sample codes below:

.top_panel_wrap .logo_main {    
max-height: 120px;
/*to enlarge header section*/
.top_panel_style_3 .top_panel_middle {    
min-height: 8.5em;
/*sticky header logo*/
.top_panel_wrap .logo_fixed {   
 max-height: 100px;
/*to enlarge top margin of menu*/
.top_panel_fixed .menu_main_wrap {   
 padding-top: 2.39em;

You edit codes above with values best fit your site needs.

Codes can be added at Appearance -> Theme Options -> Other section or your child theme style.css file or Appearance -> Customize -> Additional CSS section.