a quote from Coutts in the New York Times article:
“The major changes in my view were the balance of the boat, where obviously the load sharing between the foils is critical, so we adjusted that quite a lot,” said Coutts, an engineer by education.

“We changed that loading by manipulating the wing shapes and flaps. So we didn’t actually change anything in a physical sense. We just changed the setting, so we more bottom-loaded the wing and more off-loaded that, and that created a different loading for the foils. And that was probably the biggest change we made.

“And then there were a bunch of little changes that just reduced the drag a few kilos here and a few kilograms there, and all the sudden you have an edge.”

The article also states that " unlike Team New Zealand, Oracle sailed with a new measurement certificate — reflecting changes to its boat’s configuration — for every race as it searched relentlessly for incremental improvements."

http://www.nytimes.com/2013/09/26/sports/oracle-completes-voyage-to-history-to-win-americas-cup.html?pagewanted=all&_r=0