DIYtheme has a nifty feature where it resizes your uploaded header image or logo based on page width (s1+s2+content columns). Unfortunately, that means if your logo is created with 150 dpi or lower, your logo might look fuzzy or blurry.

Rather than battling back and forth with resizing your logo (very frustrating), simply recreate your logo with 300 dpi or higher and save it as a .png file. That will most likely solve the blurry logo issue.