How to upgrade rails 2 application to rails 3?

I developed a rails application using rails 2.3.8 version but now how to
upgrade this application in rails 3.0 version.

i think u have to change all its dependencies a/c to -v 3.0

Google for
rails 3 upgrade
and you will get many helpful links (and a few unhelpful ones of course).

Before you start make sure you have full test coverage and that you
are using a version control system (probably git).

Colin

Follow this video, may useful to You

http://peepcode.com/system/uploads/2010/peepcode-free-004-live-coding-rails-3-upgrade.mov

Possibly this railscasts would help you:

<http://railscasts.com/episodes/225-upgrading-to-rails-3-part-1>
<http://railscasts.com/episodes/226-upgrading-to-rails-3-part-2>
<http://railscasts.com/episodes/227-upgrading-to-rails-3-part-3>

Also there is another one for upgrading to 3.1 with a 3.0 base, that
could be helpfull too:

<http://railscasts.com/episodes/282-upgrading-to-rails-3-1>

HTH
Norbert