Updating Ruby 1.9.3 -> 2.0.0 without losing gems

Updating Ruby 1.9.3 -> 2.0.0 without losing gems

Have had 1.9.3p194 (RubyInstaller) with Ruby on Rails and all kinds of
Gems installed on my WinXP. Now I want to update the whole setup.
Updating RoR (to 4.0.0) and gems was easy: gem update rails, gem update
--system, gem update.
But how do I do that with Ruby? Is there an easy way to update the
installation?
If not, and I have to install the fresh package, then how do I do it with
little hassle?
I have downloaded the fresh 2.0 RubyInstaller. I have read that I
shouldn't install this new Ruby version in the same directory as my old
Ruby version (c:\programs\Ruby) that's why I chose a c:\programs\Ruby200
directory. During the installation I clicked on every additional setting,
including the "include new directory in the PATH variable" type of choice.
But now when I type ruby -v I still get 1.9.3p194 and the new directory is
absent from PATH (I haven't rebooted, so maybe this has something to do
with it).
So how should I really install the new version? Should I simply change the
old PATH to the new one? Or should I instead only add the new one without
removing the old path (so there will be some kind of advantage of having
both 1.9.3 and 2.0)? Or should I simply delete both installations and
install 2.0 from the start?
How do I easily transfer the gems (or the list of them, so the gem update
could handle the installation/updating) from my old installation to the
new one?
I am using JetBrains RubyMine 5.4 editor, and would like to know if I need
to do something there as well (for both the new and the existing
projects).