Retired old PC. Can't activate Internet Security on newer pc. Limit met

how can i activate norton internet security on my newer computer when I have met my limit of activations? I do not use my old computer on the internet any more. I currently only have Internet Security on one PC only. Used one activation on mother-in-laws PC to fix her problems. She now has her own subscription. One copy I am using now on my laptop. Third is on older PC, or should I say was. Still have 177 days left on subscription.