rvm command not found

I installed rvm with rails, from the official website of RVM, I specified the command suggested by the tutorial.When the installation my system has rails 4.0.0, rvm 01/23/12, ruby 2.0.0, bundler gem 1.3.5 and 2.0.3But I need to install ruby 1.9 to practice with a course that I am currently doing. "Rails for Zombies 2"I try to execute the instruction rvm install 1.9.3 and the console returns this message:rvm: command not found