How to renew self-signed certificate on Exchange 2k7 server

To renew a self-signed certificate, use this pshell command:
 
Get-ExchangeCertificate -Thumbprint 67455EECD51C972C2DFDAE56CF927B8851C73048 | New-ExchangeCertificate

To remove the old certificate use this command
Remove-ExchangeCertificate with the thumbprint value of the old certificate for eg:

Remove-ExchangeCertificate -Thumbprint  E3ED4FE364679696969AF93148A024669AE4CF4E