Change your logo size by following these simple steps:
Click on the Website tab at the top.
Hover over Site Design and click Header from the navigational drop down menu.
Change the value of Logo Height to increase or decrease your logo size. (Logo height cannot exceed 148px when a default logo is being used. Custom logos uploaded to the Website section can use any image size.) This field must have "px" behind the height of the logo otherwise this will not display correctly.