title: Changing a Github pull request
body: <p>As a newbie to Github, I've just submitted a pull request. The owner of the project is pretty happy with my additions but they're not quite perfect and need a bit of changing.</p>
  
  <p>How do I proceed from here? Do I need to close the current pull request and submit a new one? Or is there a way of amending one?</p>
  
  <p>Also is it preferable to reset my branch and make the required changes from scratch, or make another commit to my branch to amend the changes on top of my previous changes?</p>