The below might be of more use to you:
http://www.symantec.com/docs/DOC9324
This is the upgrade guide for 3.4.0, released a couple of months back.
It should be as simple as:
- Download PUP from FileConnect
- Upload PUP to SEMS
- Upgrade SEMS
Obviously, follow the best practices for backups and preparation as described in the guide beforehand and whatnot.
Once upgraded, the new client is automatically available from the SEMS. By default, the policies are set to notify managed clients that a new client version is available. At which point, all client machines will receive a notification (which can be disabled).
The client download from the SEMS is a MSI, and can be distributed using whatever means you see fit. The below article contains links to silent deployments for the client and stuff:
http://www.symantec.com/docs/HOWTO101963