So you signed up for an account a while ago but you've decided that you want to chose another avatar or change your password. Well that's totally fair, and you can absolutely do that!
NOTE: You need to make sure that your teacher isn't running a Gameshow when you access your account.
NOTE 2: You also need to have given your parents access to track your Gameshows to get to the dashboard.
Go to khmath.com and login to your account. You'll be brought to a screen where you need to click a "Replay GameShows" button.
Once you've done that, go to the bar at the top of the screen, click on your username and then select "Account Settings".
You'll be brought to a screen where you can change your password, add a phone number or email to your account and, change your avatar!
To change your avatar, click "Change" and all the other avatars will appear. Then just chose the one you want, click "Save" and voila!