On the US version you touch the little DS symbol on the bottom screen then go to the wrench like symbol, then the world symbol and US is in the Top left hand side.
Somewhat useless from gamefaqs
1. Turn on the DS (press the button marked "power")
2. Touch the touch screen to pass through the warning message.
3. You are now at the setup menu
4. The first option is to select a language, touch the language of choice, and
then press accept.
5. The next option is to tell the DS your nickname. Using the on screen
keyboard, type your name, then hit enter
6. The next option is your favorite color. Press your favorite color, and hit
accept on the touch screen.
7. Next option is to set the time. Using the touch screen, set the DS's time,
in military time. (if you need help with military time, see the military time
question in the FAQ)
8. Last step is setting your birthday. Using the touch screen, set the day,
and month of your birthday. (there is no option for year). Touch accept on the
touch screen when done.
9. Congrats, your done. The system will now shut down, upon which you can
start it up, and find out exactly why touching is sooooo good.
Q: You just said the default languages are different, if I got the Japanese
version, how do I change it to English?
A: you can use the handy-dandy "changing your settings" (or similar phrase)
section. Once there, I've nicely listed SYMBOLS in addition to words, to make
your life easier. THIS IS WHY I AM BETTER THAN THE INSTRUCTION MANUEL, DON'T
FORGET IT!!!!