They do not need to be uninstalled if they are using a version on a supported migration path. See the following:
Title: 'Migration paths for Symantec Endpoint Protection 11.0'
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007091315222248
Aravind's links describe methods for pushing out new packages to SAV clients using the SEP Manager (SEPM). I'm not sure what you mean by SCCM.
Here's a handy guide if you're familiar with SSC, but of course you will need to get the clients migrated over first :)
Title: 'Symantec Endpoint Protection Manager reference guide for Symantec System Center users'
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007021509381848
sandra