This is a pretty leap. It is best to create a new rails 3.1 application and then manually port your code.
gem install rails
gem install bundler
rails new myapp
, , Gemfile , , gem , ( vendor/plugins). , (mysql2, sqlite3 pg).
, , bundle install, .
, , , . , , , .
config/application.rb . environment.rb .
routes.rb Rails 3. , , Rails 3, . .
Rails 1, , , . Railscasts, , .