You need to delete the old SSL certificate and then create a new SSL certificate. You also need to check each service to make sure they are setup correctly to use the new SSL certificate. You can use anything in the fields that's appropriate and these don't have to be anything specific other than the common name which must match the domain used to access the mail server (e.g. mail.yourdomain.com).
The fields in the certificate may appear a bit cryptic to you as "o=organisation" type value pairs in the details of the certificate. As I said you can use anything you want for the fields other than common name but if you send me the old certificate to
chris@code-crafters.com I'll detail what each of these actually relates to so you can reuse the information if you want to.