Please note in order to remove the ThriveCart branding from your templates are you are required to own the Client License.
To enable this feature you can do so within the product settings. Head over to Checkout > Customize tab, then at the bottom of the cart builder you’ll see the option for Edit footer. Clicking this will enable you to select whether or not to show the branding.
To find out more about the client license you can visit this article.