Need SEPM to be Upgrade from 12.1 to 14.1

Hi, There

Recently I have a SEPM server running fine (204 Clients) with SEPM 12.1. However, due to some clients PC having licenses expired. And newly purchase licenses had became version 14. It looked like I am be enforce to upgrade current client to latest version 14. Kindly advice the procedure to upgrade the SEPM & Client licenses. I have total of 19 licenses in Version 12.1 haven't expire. Looking forward for your reply. 

Best regards,

    Wee