Ruby Gem Update - RemoteSourceException

If you need to update any gem in your system and you get some strange error message like the one below, maybe all you need to do is upgrade your RubyGems component.

ERROR:  While executing gem ... (Gem::RemoteSourceException)
              HTTP Response 403

I got the above error message when running the following command:

gem update --system

Another symptom that you need to upgrade your RubyGem is if you notice that the system responds different versions for your components:.
For instance, if you get this...

gem list rubygems
rubygems-update (1.3.5)
    RubyGems is a package management framework for Ruby

... and this...

gem -v
0.9.4

Go for the update and keep reading to find out how:
First, download the latest version of RubyGems from RubyForge. Get the zip file and unzip it; open your command window and change to the newly created folder containing the unzipped files to run the following command:

ruby setup.rb install 

That would be all. Check the versions and try again the update command.