If you search this on the internet, you will be able to find thousand of post. You can follow one of those methods to do the job. But with lots of troubles.
The steps that I'm listed down bellow is easier and within few minutes you will able to renew your license files.
First of all you need to download your SSL certificate from the licensing authority. This can be done by after,
1. Create a CSR and then wait for some time to generate the SSL certificate,
2. After expiring the SSL certificate, purchase the new certificate from the same portal and download that.
Once you go into the Certificate MMC you will be able to find the expired Cert and the dates.
Then Open the *.CER file as below and click install certificate. Once you are done that you will be able to see that under your Exchange or the IIS certificate list.
Sometime you have to select “Open with Crypto Shell Extensions” to open the certificate.
Then you can assign the services by right click on the assigned certificate and select assign services.