Upgrading Ruby on Mac OS X

Question

I am reading the book Programming Ruby and am looking to upgrade the version of Ruby on my computer. I run Mac OS X Snow Leopard and doing ruby -v in the command line shows I am

Answer 1

I updated the link to RVM in one of the answers, but also a quick poll of some friends doing Ruby dev currently revealed a preference for rbenv as a ruby environment manager: http://github.com/sstephenson/rbenv/