Why are you so intent on removing the Zen Cart copyright information? Are you ashamed of it or something? Or do you not like the free software you're using on your site? If you don't like it, you don't have to use it.
You are bound by the GPL software license (remember that license screen you had to read when you installed Zen Cart?) to retain Zen Cart's copyright details in all the code files.
You may remove the **display **of Zen Cart's copyright from the footer of your site's display to visitors via their browser and emails by altering the appropriate notices in the language files where the copyright details are generated ... only if you have changed the layout and used all brand-new graphics (not those supplied by Zen Cart) in your template or site design.
However, the copyright details **must **be kept in all the PHP file headers.
And in the admin, the Zen Cart copyright must be kept and displayed as originally written.
There is more clarification in other forum posts and also in this FAQ:
https://www.zen-cart.com/tutorials/index.php?article=42