Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
Could you please provide the following info.
1) Total number of clients in the network including managed and unmanaged clients?
2) Go to the license tab and see total how many seats are purchased?
3) It's a Enterprise Edition or Small Business Edition?
Ideally, upgrade is free of cost to all license customers. You can apply an existing license to a product upgrade.
Can refer this article: SEP 12.1 & license concept.
http://www.symantec.com/connect/articles/sep-121-and-license-concept