title: writing a Rake task for renaming a field name in a table in a Rails application
body: <p>I am very new to rails application. I need to change the column name of a table .. 
  SO i browsed thru some sites and as thy mentioned i thought of writing migration file .. </p>
  
  <pre><code>  class RenameNameToFirstnameInUsers &lt; ActiveRecord::Migration
      def self.up
        rename_column 'users', 'name', 'first_name'
      end
  
      def self.down
          rename_column 'users', 'first_name', 'name'
      end
   end
  </code></pre>
  
  <p>How to save this file and where ??</p>
  
  <p>applicationname/db/migrate/</p>
  
  <p>In what name i can save this ??
  As far now i have seen many files there but all those have prefix of some big_number</p>
  
  <p>And after saving this , how do i test it in my local??</p>