Hello Corkgirl, If you upgrade you'll have to pay the difference from what you paid when you booked your inside cabin to what the current price of a balcony cabin is. Here are the current prices for the Oct 4th sailing on the Liberty:
Interior—$699 Outside—$1,049 Balcony—$1,580
You'll have to contact your travel agent to make any changes. If it were me, I'd put that money away for the next cruise. The price difference I see would almost pay for another cruise.