Build something that works
You should check out this article on migrations, especially Section 2.1 on standalone migrations: http://guides.rubyonrails.org/migrations.html
You can remove a column by generating a new migration in the form of 'rails generate migration RemoveXxxxFromYyyy xxxx:DATA_TYPE'. In this specific case, you should type 'rails generate migration RemoveAddressFromOrders address:string'. Don't forget to do 'rake db:migrate' (or 'heroku run rake db:migrate') to run the migration and then restart your Rails server!