title: Upgrading rails to the latest version from 2.3.5
body: <p>The command:</p>
  
  <pre><code>rails -v
  </code></pre>
  
  <p>gives me <code>Rails 2.3.5</code>.</p>
  
  <p>How can I upgrade to the latest version? I have tried <code>sudo gem update</code> but get "nothing to update".</p>