One of the great things about WordPress is the number of themes that are available to change the look of your blog. There are both free and paid versions available. Changing themes is quite easy.Finding just the right theme to fit your blog can be frustrating. And that is putting it mildly.You find one that you like just about everything but that one little thing.
Change your header
In your theme folder you will find an img or images folder depending on which one the theme author used. Inside that folder will be an image called header.jpg or header.gif. You can easily grab a copy of that image and check to see exactly what size it is.