I am looking at purchasing a product key but are not entirely sure what key to purchase. If I purchase the base lifetime 20 dollar key, am I able to pay an additional 20 to upgrade that key for more game instances and such? Or will I need to buy another lifetime key?
Yes, you can pay the difference to upgrade from Professional to Advanced. I personally did the same except from Standard to Advanced. Licenses also stack, so you can buy two Advanced keys for a total of 100 allowed instances (50 + 50).