In Cakecious theme, you might want to remove/modify the white Background of logo, as seen below.

To change white circle, please put below css in Appearance/Customise/Additional css and use different image URL full absolute URL will be better.
.main_menu_area .navbar.navbar-expand-lg .navbar-brand:after {
background: url(http://your-domain/img/logo-circle-2.png) no-repeat scroll center center;
}
To remove white circle, please put below css.
.main_menu_area .navbar.navbar-expand-lg .navbar-brand:after {
background: none;
}