Grateful, already
You have to add your images to the theme you are using. Take a look at the theme folder and see how it is contructed. Create your new logo and add to themes/default/images and then change old one to something like logo.png.old then change your new picture file to logo.png .
What you have to do is take a look at the default images and see where they are and sizes etc.
Then just replace them with your new ones. Once you are satisfied with your new images then delete the old ones.
Good luck!
Ken
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