In the Symantec Endpoint Protection Manager console, click Admin.
In the Admin page, click Servers.
In the Admin page, under View, click the icon that represents the MS SQL or embedded database to be backed up.
In the Admin page, under Tasks, click Edit Backup Settings
you can select the number of backups you want to keep so that it will wutomatically delete the older backups.
Or also you can follow this documet to change the folder for back file
Published Externally
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2008010223062548
Plase mark this as a solution if this works for you.:)