Converting Single Licenses to Multi-License Pack

I have two separate PC's running AntiVirus 2012 under single separate licenses. Adding a (new) third PC, how can I convert existing licenses into a license pack?

 

Do I purchase the "3 license pack", delete the Norton Product from the two current PC's and then install Norton Product onto all three PC's with the New Product Key?

 

I have 9 months on one PC, and 23 months on the other PC. How best to combine under one license pack? Any help, or clarity, is appreciated.

 

Steve