title: How do I update Ruby-interpreters with RVM?
body: <p>I installed RVM with a few versions of Ruby-interpreters some time ago.
  How I can to update it, because new versions are already released?</p>
  
  <p>I found only one way: <code>rvm install 1.9.2-rc1 &amp;&amp; rvm remove 1.9.2-preview1</code>, but my gems are lost.
  Can I update branches time to time? I haven't found any tips in the documentation.</p>