Hello,
In order to remove the advertisement, you would need to put the certificate you have purchased in the root folder on the web server. If you have tried the demo certificate, you would have to replace it with the full one.
Please also note that the certificate must be visible when you load its web address in the browser and the MIME type must be plain-text.
In case you need to place the certificate in a sub-folder on your web server, then you will have to use the CheckCertificate() method from the API documentation.