title: how to update express to version 4
body: <p>I just tried to update my version of express to <code>4.0.0</code></p>
  
  <p>I used <code>sudo npm install -g express</code> and I can see the newest version has already been installed on my laptop.</p>
  
  <p>However, when I type <code>express -v</code>, the version is still <code>2.5.8</code>. How to change it to <code>4.0.0</code>? </p>
  
  <p>Thank you</p>