backup 2012 agent question

 I currently have Symantec backup 2012 on a win 2008 R2 server (non-domain setup). It backs up the main server and a qnap “server” (no iscsi drives) . It complained the other day that I do not have a license for the agent to back up the qnap server. I have no problem in purchasing the agent, but which one do I purchase and where do I install it. Thanks.

Randy