Admin Help

[Rybena]

Hi
I am wanting to know if it's possible to change the admin name from openvpn to something else. Or even better if I can disable admin login from outside the server eg I only want clients to be able to log in from off-site not the admin.
My concern is that if the admin name can't be changed then that's more vonerable to attacks and only the password needs to be cracked and not the admin name as it's always openvpn.

Thanks in advance.