Go to the Server Management screen.
Click the green icon (Wrench for RaQ4, Pencil for XTR) next to the SSL enabled virtual site
Click SSL Settings on the left side.
Copy the entire contents of the site certificate that you received, including
-----BEGIN CERTIFICATE-----
and
-----END CERTIFICATE-----
Paste the new certificate information that you copied into the "Certificate" window.
Select Use manually entered certificate from the pull-down menu at the bottom.
Click Save Changes.