HI,
You can Create New Group and Move Sep client which system do you want to Upgrade.
You can use AutoUpgrade Feature
Upgrade clients to SEP 12.1 by Auto upgrade feature
http://www.symantec.com/connect/articles/upgrade-clients-sep-121-auto-upgrade-feature
Upgrade clients to SEP 12.1 using Auto upgrade feature
http://www.symantec.com/connect/videos/upgrade-clients-sep-121-using-auto-upgrade-feature
Note :You must test the AutoUpgrade process before you attempt to upgrade a large number of clients in your production network. If you do not have a test network, you can create a test group. You can add a few non-critical clients to the test group and upgrade them by using AutoUpgrade. You can confirm the upgrade completed successfully by verifying the version number of the client software that appears in the About dialog box.