HI I created a Ruby on rails migration file as follows and in the first stage I created tables 

then I want to add columns and remove some columns and I modified it as follows 

```
class CreateMt940Batches < ActiveRecord::Migration
  def change
    create_table :mt940_batches do |t|
     t.string :account_number
     t.string :transaction_reference_number
     t.string :information_to_account_owner
     t.string :file_name
     t.binary :raw_data_transaction
     t.string :sha1_checksum
     t.timestamps
   end

   def self.down
     remove_column :account_number, :transaction_reference_number, :information_to_account_owner
   end

   def self.up
     add_column :mt940_batches, :created_by, :updated_by, :integer
   end 
 end
  end

```

but when I ran rake db:migrate nothing has happens. How to accomplish this task . I want to change the model already created as well from this migration file. Um looking a way to do this. Thank you in advance