Hi @cgmt ,
Thank you for using Estera theme. This option is available in the pro version of the theme: https://nasiothemes.com/themes/estera/
I would really prefer that you keep the credits, if you plan to use the free version of the theme only. If you really need to change them, this can be done via a child theme, by editing the footer.php file.
Please note: do not attempt to alter the theme files directly, as this will get overriden by the next theme update. I hope this helps!