title: How to get Wix to update a previously installed version of a program
body: <p>I wrote an install program with Wix and it worked fine to install my program.
  Now I need to update it, so I bumped up the version number but when I go to install the new program over the old one it complains that an older version is already installed and tells me to uninstall it first.</p>
  
  <p>How do I get it to update or automatically uninstall it before reinstalling?</p>