update rubygems

I tried to update rubygems on CentOs but could not.
First, I asked help to my friend Google and found this site: http://rubygems.org/read/chapter/3
It worked well on one computer but on another one I had this error:

/usr/lib/ruby/site_ruby/1.8/rubygems.rb:578:
in 'report_activate_error': could not find RubyGem session (>= 0) (Gem::LoadError)

I tried many things until I realized that "session" is actually a gem!
So let's do:

gem install session

Another error "could not find RubyGem hoe-seattlerb..."
So let's do:

gem install hoe-seattlerb

Same error with "hoe". But this one is tricky, because hoe need rubygems > 1.3.1, but to install rubygems 1.3.5 we need hoe!

update_rubygems
/usr/lib/ruby/site_ruby/1.8/rubygems.rb:578:
in `report_activate_error’: Could not find RubyGem hoe (>= 2.3.0) (Gem::LoadError)

gem install hoe
ERROR:  Error installing hoe:
      hoe requires RubyGems version >= 1.3.1

I tried to do (wihout success):

gem install rubygems-update #by default, it installs the latest version which is 1.3.5 now
update_rubygems

The problem is in version 1.3.5! First remove all rubygems:

gem uninstall rubygems-update

#Then
gem install rubygems-update -v 1.3.4
update_rubygems

#Then you can install hoe
gem install hoe

I lost so many hours for this stupid mistake...