When using an SSL certificate to secure a web site, you can typically choose to “renew” an existing certificate with the original certificate authority. If you decide to switch SSL providers when the time comes to renew, you cannot simply choose to “renew the current certificate”. You need to generate a new CSR for the site, but do not have that option available if an SSL certificate is currently associated with the site. Removing the current certificate in order to generate a new CSR is typically not acceptable.

You can create a new virtual web site in IIS and use it to generate a CSR to use with the existing live site. TI created a document that walks you through that process. You can download it from the Technical guides Tab or directly from here at Install a SSL certificate on IIS when you cannot use the renew certificate option