the header of the pages in the Community blog template is managed by a HTML webframe called "blog header" and is in fact an image.
To change it you need to follow these steps:
1. Log in with an account that has Architect, Manager or Builder role assigned.
2. Once logged in you will be able to enable the smartbrowse mode by clicking "enable smartbrowse" in the lower left corner of the screen. (if it is already enabled skip that step)
3. Once in smartbrowse just right click with your mouse on the header of the blog and in the context menu select "Manage" (the title of the context menu should say "blog header"
4. You will be redirected to the webframe management screen which is in fact a web text / HTML editor.
5. Lesft click on the image to select it, than Right click on it and select "insert /edit image"
6. You can paste the address of the new image in the "image URL" field or click on the browse icon to upload and select new one.
7. Save your changes.