How to Upgrade Your Ruby on Rails Application
Ruby on Rails evolves quickly. It may not look like that, but when you go back to your applications, you find them most likely a few versions behind the current stable release. Unfortunately, you cannot simply jump from your current version to the newest one. Instead, you need to upgrade from one major version to the next one (for example: from 4.2.6 to 4.2.11, then to 5.0, 5.1, 5.2). That means the longer you wait, the more work will it take to get to the newest version.
The official Upgrading Ruby on Rails guide explains the required steps in all the details you need to know. However, there are few obstacles I run into that you do not need to repeat.

