Search for your cabin using your booking number and keep entering in the room numbers until your cabin number comes up.
The Kelly Method is a way of discovering the cabin Carnival has you assigned in if you have booked a guarantee category. Although this is not a guarantee that you will end up in the cabin, most of the time it works out.
To do this you need to have your booking number from Carnival. Go to Carnival's website and go to the Gifts and Services section. Pick an item and proceed like you are going to enter it. A screen will come up that asks for your cabin number and booking number. This is where it becomes time consuming. Enter your booking number and grab your Carnival brochure. Start putting in numbers for cabins in the category you are booked in. When you enter the correct number your information will pop up. If you go through all the cabin numbers in the category and nothing comes up go to the next category. Just work your way through until you find your cabin. It is time consuming but a great way to waste time until your cruise!
A couple of disclaimers...
Most upgrades occur within a category (4A to 4B etc.) so if you book a 1A I wouldn't start by looking at the category 11 and 12 cabins!