How to Change Login Credentials (User Name) from mail to value?

Hi all,

I need to change the login "User Name" from the email that is currently asking for and use the First Name or a new field if is possible. All users were created with the email as user name ((first.last@yourdomain.com) Your E-mail Address will be your User Name ).

For example:

Now User Login: hector.garcias@cummins.com

Future User Login: hectorga

Is it advisable to make this change?

If I can and don't break anything, where can I do it? I have not had good experience making changes related to user data.

Thanks and regards,

Hector Garcia