That time of the year, Certificates expiring, exchanges could be breaking and many more. How to Renew or Generate a new CSR for a WildCard Certificate using Exchange 2010 / Exchange 2013. They both have different steps but it’s the same outcome,
Step-by-step guide

Mircosoft are actually pretty decent in making this a easy IT Administrator job for any level, but you need to ensure the details you enter are correct or could be an expensive incorrect wildcard.

1. Log into your Exchange Management Console (2010/2013)
2. For Exchange 2010 Click on Server Configuration, your see the servers and Certificates attach to it..
3. Click New Exchange Certifiate, this is a boucning ball process, input Name for Certificate Click Next.
4. Tick Enable WildCard Certificate, Put in domain (Amouxit.com ) as an example..
5. Fill out the details, required. Browse where you want to save the REQ file.
6. Gernally, depending who you go through you would open the REQ file and copy the entire contents into the browser and it will then create the Certificate based on the information provided..

That’s pretty much it for 2010, 2013 is very similar article can be found here: https://technet.microsoft.com/en-us/library/bb125165%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396