Editing the { } variables, ex. {vb:raw facebook_header}

[cellarius]

The values of those variables is set in the php files and then passed to the templates. Do a search over all files for "facebook_header" to find out what file exactly you need to look at. You may even be able to do what you want using a plugin at a hook without hardcoding anything. (Whether the facebook image can be easily changed I don't know, I think that's served and controlled by facebook itself).