crop site logo

Hi everybody, hope someone can help me as soon as possible… I need to insert a logo in my page: I thought to use “image logo” option in Appearance -> Header to insert it, but the defined size for this image is 90×300: I need to insert a 930×300 image. I’ve modified style.css:
`img.site-logo, h1.site-title {
color: #B81005;
float: left;
font-size: 80px;
font-weight: bold;
letter-spacing: -7px;
max-height: 930px;
max-width: 300px;
padding: 5px 0;
text-shadow: 1px 1px 1px #000000;
word-wrap: normal;
}
`
but when I insert the image, it crops it in 90×300. How can I modify php files to insert a 930×300 image?
I hope I’ve been clear enough! Thanks!

Chiara