How do room upgrades work

[Love to Cruise DCL]

Ok this is funny coming from a "veteran" DCL cruiser but...
I have seen mention of people upgrading when they check in...how does that work with DCL?
We almost always book 4A but did not this time and our ship does not seem to be full...so I thought maybe we could get a 4A when we get there.
Any insight from someone who has upgraded or knows how this works would be most appreciated

Steph

 

[OKW Lover]

When you check in at the port, ask about the possibility of an upgrade. You'll be directed to a separate counter to find out how much this will cost if available.

 

[timandlesley]

When you check in at the port, ask about the possibility of an upgrade. You'll be directed to a separate counter to find out how much this will cost if available.

Do you know if you've booked an IGT if they will base the increased price on the discounted rate you booked at? Will we be charged MORE to upgrade? I'm hoping we can upgrade but I can't spend a fortune on it. Any cost examples of upgrading at port anyone??
Lesley