depends on your subscription, but in general Stardock software requires resubscription when going from, say, 4.x to 5.x
If your subscription is active (to Object Desktop) and you're using Impulse to update...if you're entitled, the update should appear as 'available'.
Since your version (4.21) is fairly old, I'm suspecting you might well have to buy. I could be wrong...ask sales@stardock.com
