title: Update android app with apk package from external source
body: <p>We are developing an Android app and I made an apk available through a web site for our pilot users. The users have Install from unknown sources setting enabled. The app installed and worked fine.</p>
  
  <p>Now I uploaded a newer version of the app. We have changed the version number on the apk package and the new version requires more permissions from the phone, like Prevent phone from sleeping when the first version only needed Full network access.</p>
  
  <p>When I download and open the new version it says "Do you want to install an update to this existing application... Then updated application will get access to:" and then lists the added permissions under a New tab and all permissions under All.</p>
  
  <p>So the installation identifies that this is an update and what has changed in terms of additional permissions.</p>
  
  <p>When I go forward with the installation the installation stops with the message "An existing package by the same name with a conflicting signature is already installed".</p>
  
  <p>What do I have to do/change to be able to upgrade the existing app?</p>