Upgrade from Ruby 1.8.7 to Ruby 1.9.2 on Ubuntu

sudo apt-get remove ruby1.8 ruby

# this is actually Ruby 1.9.2

sudo apt-get install ruby1.9.1 ruby1.9.1-dev 

sudo ln -s /usr/bin/ruby1.9.1 /usr/bin/ruby

Now, Install RubyGems

sudo apt-get install rubygems1.9.1