Change the "from" field

Hello,
I used some random word to create the account ID to later host the domain based emails. That username shows up in the "from" field on test emails.
How do I change that to a custom one, like first name/last name or business name?
I tried to create second user and "named" it the way I want and it worked to a degree, although the "from" field shows all lower case letters, while original had some capital letters. So the "all-low-case" is another issue I am having...

Thank you