Remove the current cert from the IIS website, then delete it out of the Cert MMC snap-in for the Local Computer.
Start a new cert request from IIS, pass info to CA and get back new cert.
Install Cert into IIS, using port 443.
Once cert is installed the website will be stopped, modify properties removing the SSL port (field should be blank) and save. Website will now start.
I’m not sure if this next step is necessary:
Open Secure Gateway Management Console and run Configuration, pick defaults and verify cert selected is correct.