Enterprise Vault 8.0 SP4 is a full product release and can only be obtained from the Symantec Licensing Portal.
http://entsupport.symantec.com/docs/292866
You will want to follow the steps in the Microsoft cluster: installing the Enterprise Vault server software section of the Enterprise Vault Upgrade Instructions.chm/pdf that is part of the release notes.
Release notes can be found here:
http://seer.entsupport.symantec.com/docs/337274.htm
Be sure to note this issue when upgrading: http://seer.entsupport.symantec.com/docs/323904.htm