Hey there! cPanel isn't designed to be a web page editor, but you can use the File Manager tool (File Manager | cPanel & WHM Documentation) to open and edit files directly from the cPanel interface without needing an FTP client.
If you want an entirely new website to replace what you have, we also have the Site Publisher option as well - Site Publisher | cPanel & WHM Documentation
If you want an entirely new website to replace what you have, we also have the Site Publisher option as well - Site Publisher | cPanel & WHM Documentation