If you ever need to change the name of your account, you can do so in the General settings.
You need to be an Account admin to access the general settings.
Under the section General, you'll find the section "Name". Change the name of the account, and click "Save general settings" to save your changes. 
By default, the name of your top group in the hierarchy will have the same name as your account. If you change the name of the account, the change will not apply to the top group in the hierarchy.
You need to manually change the name of the top group in the hierarchy, if you want to change the name.
You can change the name of any group by clicking the name of the group, and selecting "Edit group".
