The flag set on your profile will always correlate to the country in which your account was set up. This flag is visible to you when you log in on your main page. It is also visible when you are playing Live Mathletics and in the Local and Global Hall of Fame. If you are using an account at School your flag is the same as all of your classmates and cannot be changed in any way.
If you are using an account at home the flag on your main page cannot be changed, but the flag that represents you in Live Mathletics can be changed. You cannot change it yourself; you will have to ask your parent or guardian.
For your parent or guardian to change this they would need to log in to log into their account and click on EDIT by your name. They will then see a drop down menu where they can choose the flag they wish for you to represent in Live Mathletics.
Please note that changing this flag does not change the flag on your main page. It will only change the flag shown in Live Mathletics.
This means that you and your opponent can see the flag your parent, guardian or teacher has set it to when competing. However, if you make it onto the Hall of Fame, the flag shown will still be the same as where your subscription was set up.