NIS 2010, renewing annual license question

I have NIS 2010 (1 yr, 3 pc) installed and running fine on Win 7 and XP machines. My current license expires in in about 30 days.

 

I also have a new, unused but different license code, NIS 2010 in a factory box. I want to use the new NIS license code to update my soon to expire NIS.

 

What is the easiest way to do this? I don't want to delete and re-install unless I must.

 

Thanks,

 

S.