Change Default Text on Header.php in WP-ADMIN

Is there a way to alter the default text on the header.php page for the Twenty Twelve theme in WordPress?

You can select an image to be shown at the top of your site by uploading from your computer or choosing from your media library. After selecting an image you will be able to crop it.
Suggested width is 960 pixels. Suggested height is 250 pixels.

I’d like to change up the size and the wording.