prospect and how to go about an upgrade to balcony on Sinfonia in May

We have a booking on the Sinfonia for May next year (Venice, Slovenia, Croatia, Ancona. Venice ) in an Inside Fantastica. As it is my 70th birthday in February one of my sons has offered to upgrade us to a Balcony. Not sure what the prospect is of doing this and whether I go to the TA (CruiseNation) or direct to MSC. My other anxiety is whether there would be a large charge for changing the booking on top of any difference in price.

I have a recollection of adding a granddaughter to a booking a few years ago and the cost of changing the booking being as much as the charge for her being in the cabin.

In my experience, upgrading rooms on the same ship would not incur any change fees. You should contact your TA, which you actually can't even mention here, so this post may be deleted.

You can upgrade but the cost will be the difference between what you booked at and the current balcony price. Also, they will insist you go through your TA. Not so many balconies on Sinfonia so best not delay. Ken

Thanks both of you for your responses. Contacted TA today but MSC have told TA that all the Balcony Cabins are already booked up but can try to enquire again nearer to date of cruise to see if there have been any cancellations.