There are 2 options.
1) Settng up LUA (LiveUpdate Administrator) as mentioned in the below link. This involves a lot of data (in GB). This can be useful in a network where you have Windows as well as MAC. Also this will update all the definition (Not just AV, SONAR and IPS).
http://www.symantec.com/docs/TECH106254
2) Updating the SEPM using JDB files. Currently Symantec provides (3 seperate) JDB files to update the AV, SONAR and IPS components. This will only update machines with Windows OS. The size of the JDB files would be as follows:
AV : ~640 MB.
SONAR : ~ 4 MB
IPS : ~5 MB
SEP clients on MAC can be updated using the file at the following location (~1350 MB):
http://www.symantec.com/security_response/definitions/download/detail.jsp?gid=nmc