You can change your sub-account name/url by navigating into the account settings.
Click on your current account name in the top left corner of your dashboard (V2) and click on the “Account Settings” button.
You can get to the same page by clicking on the “Settings” button in the main menu on the left.
You will be presented with the form for changing your account details.
Input new globally unique account name, keep in mind account names can be changed only once every 30 days and it will change all media URLs associated with this sub-account.
Simply click on the “Save Changes” button to save your new sub-account name and URL.