Deleting the footer credits are not allowed and doing so will get your blog suspended. Which upgrades you have makes no difference to this – even WordPress VIP clients that pay $5000 a month are still required to show those footer credits on their websites.
11. Attribution. Automattic reserves the right to display attribution links such as ‘Blog at WordPress.com,’ theme author, and font attribution in your blog footer or toolbar. Footer credits and the WordPress.com toolbar may not be altered or removed regardless of upgrades purchased. https://en.wordpress.com/tos/
You are allowed to add your own information to the footer as long as the WordPress and theme credits remain visible and clickable. You can do that by adding custom CSS to your site (the Custom Design upgrade is included in Premium).