Once the previous steps have been completed you should have your default system version of Ruby and the new version of Ruby installed. You can view all of your installed versions by typing:

rvm list

You can tell your system that you want to use a specific version of Ruby by typing:

rvm 1.9.3

Typing:

ruby -v

will confirm which version of Ruby is currently active.

If you want to make something other than the base systems version of Ruby the default so that you do not have to switch to it every time your reopen the terminal, you can type:

rvm --default use 1.9.3