I definitely recommend installing the Rails upgrade gem (rails upgrade gem). It's proven for me to be incredibly useful as a starting point for listing and verifying all the required upgrades to get to Rails 3.0.
This won't be a simple task and you'll need to ensure that your code doesn't break at each step, but these are tools I've found were great to get the ball rolling.
Please refer the link, http://www.spritle.com/blogs/2013/02/08/upgrade-rails-2-application-to-rails-3/ It may helpful to you.
I definitely recommend installing the Rails upgrade gem (rails upgrade gem). It's proven for me to be incredibly useful as a starting point for listing and verifying all the required upgrades to get to Rails 3.0.
I would also recommend this ebook http://www.railsupgradehandbook.com/
Once you're at Rails 3.0, you'll need to migrate to the asset pipeline, this is another good starting point: http://railscasts.com/episodes/282-upgrading-to-rails-3-1
This won't be a simple task and you'll need to ensure that your code doesn't break at each step, but these are tools I've found were great to get the ball rolling.