By default, your forum username will be the same as your Arduino account. If you prefer to use a different username in the forum, this can be configured in the forum preferences. Follow the steps below to change your forum username.
When you can change your username
After registering your account you have 3 days to change your username.
How to change your username
Go to the Arduino Forum and log in to your account.
Click on your profile picture in the top-right to open the menu. Click the tab, then click on Preferences.
Under Username, your current forum username will be displayed. Click the pencil icon next to it.
Enter a new username and click on change.