Site name

Edit the site name in the Site settings > Site content > Site name.  This usually displays on all pages, and is used in the search optimization of your site.


 

Custom image

A custom image can be displayed in place of the name by going to Site settings > Site content > Site name > Custom image tab > Upload image...
 

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NOTE:
If you decide to use a custom name image, or not display the site name, it's still important to enter relevant text in the Site name field for search engines.