How to increase the size of the logo?

In order to increase size of the logo you need to add the following CSS statements to Custom CSS field of Appearance > Customize > General panel:

img.btMainLogo {
    height: 50px;
}
.menuHolder .menuPort {
    margin-top: 15px;
}

Please adjust the numbers according to your needs. The first number (50px) represents the height of the logo and the second (15px) represents the top margin between the header widget elements and content.