title: How to upgrade big Ruby on Rails project from Rails version 4.2.2 to 6.0.2.2?
body: <p>I have a huge rails web application with wide user base which runs on Rails 4.2.2 and Ruby 2.2.2 as of now. I simply want to upgrade the whole application to the latest version of Ruby i.e. 2.5.0 and Rails 6.0.2.2. 
  The reason for upgrade being I want to integrate a completely separate React.js frontend and a separate Rails backend. Other reasons for upgradation being deprecating older version of gems and rails. 
  I have tried researching a lot for this. I have also tried the : <a href="https://guides.rubyonrails.org/upgrading_ruby_on_rails.html" rel="nofollow noreferrer">https://guides.rubyonrails.org/upgrading_ruby_on_rails.html</a> guides. But everything out there is so vague and haphazard. I havent found any clear cut method until now following which I can upgrade my rails application smoothly. 
  Please help. </p>