For a simple way to renew your certificate for IIS 8, see Microsoft IIS 8 and IIS 8.5: SSL Certificate Renewal Using the Digi Cert® Certificate Utility for Windows.
How to Generate an SSL Certificate Renewal CSR in Microsoft IIS 8 and IIS 8.5 For help with your SSL Certificate installation or troubleshooting, use our Digi Cert® Certificate Utility for Windows.
To install your newly acquired SSL certificate in IIS 7, first copy the file somewhere on the server and then follow these instructions: Most SSL providers issue server certificates off of an Intermediate certificate so you will need to install this Intermediate certificate to the server as well or your visitors will receive a Certificate Not Trusted Error.
Note: These instructions apply to an SSL certificates hosted on third-party servers, dedicated servers, or virtual dedicated servers.
This new version makes several big changes in the way that SSL certificates are generated, making it much easier than previous versions of IIS.