How to Renew a Server Certificate
Server certificates are files that allow your web server to host encrypted data. Server certificates are valid for a year, so you must renew them before the expiration date. The Windows Internet Information Services (IIS) management utility has a renewal wizard that helps you create a new server certificate for your Windows website host.
Click the Windows "Start" button on your web server.
Click "Administrator Tools," and choose "Internet Information Services (IIS) Manager." This is the utility that controls your web server settings.
Right-click your website's name on the left panel.
Click "Properties" to open a settings window.
Click the "Directory Security" tab.
Click the "Server certificate" button to open the wizard window that creates a server certificate for
Click the option labeled "Create new certificate" and choose "Prepare the request now but send it later." This option renews the certificate request. You must send the request to a certificate authority, which is a third-party company that verifies your certificate and sends back an encryption file to complete the renewal of the server certificate.
Return to the server certificate wizard again after you receive your renewal file from the certificate authority, click "Create new certificate" and this time choose "Process the pending request." Click "Next."
Double-click the file you received from the certificate authority.
Click "Remove the current certificate" to remove the old certificate and replace it with the new one.
Click "Next" until you reach the final window.Source: ehow.com