Updating your rails application?

How can I update my rails application to work with the current release
of rails? For example, I had rails 0.9 and created an application. I
installed the will paginate plugin and now the application can't run.
I upgraded everything and created a new test application, installed
the plugin and it works. However, my old application doesn't work.

So basically, what I'm getting at is, each time a new version of rails
comes out, how can I update my application so that it'll reflect the
current release of rails? Thanks!

Just figured it out...for anyone else who was wondering this, it seems
you replace the config directory with the newest version (careful not
to overwrite database.yml).

This works great if you use some sort of version control like
subversion. I let the update overwrite all files it wants to then I
revert the unwanted changes.