How to change the Form1 to FormMain in Delphi

I'm starting with Delphi and I just find annoying that I get default varuables of Form1. I want to give it other name like FormMain or something like that. So let's see my code:

unit main;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  TForm9 = class(TForm)
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form9: TForm9;

implementation

{$R *.dfm}

end.

Code above works fine when I compile. Now I change next code to:

unit main;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  TFormMain = class(TForm)
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form9: TFormMain;

implementation

{$R *.dfm}

end.

And in other file .dpr I also change it to:

program mainProject;

uses
  Vcl.Forms,
  main in 'main.pas' {FormMain};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TFormMain, FormMain);
  Application.Run;
end.

And this gives me errors, what ever I change. I just want to change default form name.