You can remove the branded footer by upgrading your subscription. Here's how to do this:
1. Click on the "trash" Delete icon that appears when you hover over the footer.
2. On the next page, click Upgrade and complete the steps required to upgrade your website plan. You should notice now that the footer has disappeared.
3. Click the Publish button to save the change.
4. Once you have removed the branded footer, you can click on the Add a block + button and add a Footer block from the Block library.
You can learn more about removing a footer with a brand logo in this tutorial.