Hello,
By default the Symantec Endpoint Protection Manager downloads and keeps a particular number of virus definition revisions in its repositories based on the type of install performed:
Simple: A management server that manages fewer than 100 clients and uses an embedded database.
3 revisions
Advanced: A management server that manages more than 100 clients or if you want to customize the configuration.
Between 100 and 500 = 3 revisions
Between 500 and 1,000 = 10 revisions
More than 1,000 = 30 revisions
Reference: Maintaining the database
You can delete the legacy client packages from the SEPM console if not required.
Path: SEPM--> Admin --> Install packages
Also check these articles:
Disk Space Management procedures for the Symantec Endpoint Protection Manager
http://www.symantec.com/docs/TECH96214
Changing the log settings to reduce the size of the database.
http://www.symantec.com/docs/TECH105238
Best Practices for configuring the number of content revisions to keep in Symantec Endpoint Protection Manager
http://www.symantec.com/business/support/index?page=content&id=TECH92225