/**
 * Read more {@link https://codex.wordpress.org/Function_Reference/wp_set_password}
*/
wp_set_password( 'newpasswd', 1 );

/**
 * Create a new user with admin caps
 *
 * Read more {@link https://codex.wordpress.org/Function_Reference/wp_create_user}
 *
 * @version WP 4.7.3
 */
add_action( 'init', 'wpse262478_add_new_adminuser' );
function wpse262478_add_new_adminuser()
{
    $username = 'aname';
    $email    = 'whatever@domain.com';
    $password = 'LZTf$f$FR)Y@xye';
    $user_id  = username_exists( $username );

    if ( !$user_id && email_exists( $email ) == false )
    {
        $user_id = wp_create_user( $username, $password, $email );

        if( !is_wp_error( $user_id ) )
        {
            $user = get_user_by( 'id', $user_id );
            $user->set_role( 'administrator' );
        }
    }
} // end function