I'll answer my own question in case someone else wants to change the flag from British to U.S.
Go to the files and find the *.png files (16.png, 16a.png, 24.png, 24a.png, 32.png, 32a.png). Also search google images for a U.S. flag. Reduce the U.S. flag to 32 pixels wide and then paste it in both 32.png and 32a.png over top of the British flag. Adjust the size and repeat for the 24 and 16 pixel files.
Voila! English now has a U.S. flag.