I have installed from source Ruby in the folder /usr/lib/ruby-1.8.2/.
(I use Linux)
If I do "which ruby" I get /usr/local/bin/ruby. It seems that Ruby has
created the folder /usr/local/bin and filled it with ruby, irb, etc...
I don't mind, this is all fine.

Now my question is: when at XMAS Metz dressed like Santa will bring me
Ruby 1.8.4, how should I upgrade?

I was thinking do to the following:
1) Remove the folder /usr/lib/ruuby-1.8.2/
2) Install Ruby 1.8.4 from source in /usr/lib/ruby-1.8.4/
3) During the Installation of Ruby 1.8.4, it will overwrite
automatically the folder /usr/local/bin/ with the new versions of ruby,
irb, etc... I am not sure if it works automatically in this way. Can
you confirm?
If it doesn't happen out-of-the-box, I was thinking to create a
symbolic link from /usr/local/bin to /usr/lib/ruby-1.8.4/bin/.

Regarding Gem and Rails, I will probably just remove Gem's folder and
reinstall it. And then just reinstall the main gems that I am using
including Rails. The rails websites/application that I have done are
saved elsewhere and shouldn't be affected.

Is it a good approach? How will you do it?