Hi,
Check this article
Upgrading and migrating to Symantec Endpoint Protection 12.1
http://www.symantec.com/docs/TECH163602
On the Home tab there is an option common task, click on that you will find an option to install protection client to computers.
Easiest option would be auto upgrade, stated in attached article also.
http://www.symantec.com/docs/TECH96789