Here's the guide for upgrading a Rails app, covering versions 3.0 up to 5.0: http://guides.rubyonrails.org/upgrading_ruby_on_rails.html http://guides.rubyonrai

Here's the guide for upgrading a Rails app, covering versions 3.0 up to 5.0: http://guides.rubyonrails.org/upgrading_ruby_on_rails.html http://guides.rubyonrails.org/upgrading_ruby_on_rails.html As you can see, changes in Rails will sometimes dictate changes in your app. Sometimes there are flags that can be set (or not set) to defer some changes or alter default behaviour.