To update ruby version used by a ruby on rails app we need to start with installing the ruby version we want. This can be accomplished very easy with Ruby Version Manager (RVM).
Start a terminal window and run this to install RVM and Ruby 1.9.3:
When the install is done quit the terminal and start it again, then run this command to set ruby version:
Next update the gemfile with the new ruby version:
And we’re done!