We're offering a discount for customers who've purchased older perpetual licenses. The discount only applies when initial subscription plan is annual. If you're eligible for the discount it'll be shown on top of the pricing page once logged in.
The previously purchased perpetual licenses are going to keep working even after the subscription expires. The upgrade pricing is just a discount and doesn't change the purchased licenses.
The discount is calculated based on your previous purchases, the more licenses you own the better discount.