Original : http://www.georgealmeida.com/2016/01/renew-exchange-2010-self-signed-certificate/

Renew Exchange self-signed certificate

1. Log onto the Exchange 2010 server/s, open EMC (Exchange Management Console). Expand your Exchange Server and select Server Configuration and highlight the server/s in question. You will notice the self-signed certificate has expired.

2. Right-click the cert and select Open. Select the Details tab and then select Thumbprint. Copy or make note of the certificate’s thumbprint. You will need this in order to renew the self-signed certificate.

3. Renew the NAHQEXS23 self-signed cert using its thumbprint to identify the cert using the following powershell command. Of course, you will need to open the Exchange Management Shell as an administrator prior to excuting the command below.
Get-ExchangeCertificate -Thumbprint ‘2borb319fg55cd442bf379876xxc6c8322a58679’ | New-ExchangeCertificate

** – Note: the thumbprint is the thumbprint you made note of in step #2

Remove old Exchange self-signed certificate
4. You will notice a new self-signed certificate in the EMC. You should now remove the old cert by right-clicking on the old cert and selecting Remove.