title: pandas rename index values
body: <p>I have the following dataframe in pandas (python):</p>
  
  <pre><code>      B.  X.  Y.  
  A
  alpha 3. 5.  5
  beta  9. 9.  11
  </code></pre>
  
  <p>I want to change 'alpha' for another name, like 'mu'. What should I do?</p>