RVM allows you to install a plethora of Ruby versions and switch between them in a snap. This is a no brainer for Ruby developers as we move forward. Along with Ruby versions, RVM provides the ability to create gemsets to allow the changing of gems depending on projects.
Installing Ruby 1.9.2:
rvm install 1.9.2
Using Ruby 1.9.2:
rvm use 1.9.2
It's that easy. Here's a good installation guide. Look out for instructions after installing RVM. Make sure you do everything it tells you to, especially removing the return from your .bashrc.