Text in header changes when I install my theme

Hello everyone. I am a newbie and I am trying to learn before I post but can’t figure this out. I had a custom theme made via artisteer 2.3 and when I install the theme to my wordpress site the text in the header changes. When I deactivate the theme and preview it, the text is there. My text is “McCann Forest Products” the 2nd line is “Service and value is what we do” but when I activate it, it says “My Blog” 2nd line says “Just another wordpress site”. I don’t see any options to edit my header and I’m confused. Any help would be great. Thanks.