How do you Change character to a pokemon?

Sorry, whatever character you chose in the beginning stays with you until the very end. You could restart the game and choose again, but that would erase all of your data.

Go to "My Zone" and then "Update Profile" and you will find it there. -Kroll

there probaly is a way first i think you should get the national pokedex and then go to evrey place in sinnoh region

sort of, if u go to the Pokemon center in oreburgh then talk to the dude on the left hell ask u wat u want to look like when your in a trading zone.{only works in trading zone}

you can't unless you refresh the game.