The default Plesk page confirms that your site is working and that files are loading as they should. If your new account is less than 2 hours old, please note that it can It can take up to 2 hours for your account to be fully active. You can read more about that here: https://wiki.helionet.org/hosting/signing-up#up-to-2-hours-for-activation
To update the content of your website, you need to replace the `index.html` page with an `index.html` page that has your own content, and the changes should appear for you once the file is uploaded, once your account is a full 2 hours old.