title: Switch theme in an existing Jekyll installation
body: <p>There are many themes for Jekyll, e.g. <a href="https://github.com/jekyll/jekyll/wiki/Themes" rel="noreferrer">https://github.com/jekyll/jekyll/wiki/Themes</a>.</p>
  
  <p>What is the easiest way to switch to a new theme in an EXISTING Jekyll installation?</p>