title: Can't change username and password from git
body: <p>I use git extension.
  I wanted the password and username to be store in cache so I used: 
  git-credential-winstore.
  It worked fine until I had to change the password in my computer (win7) and it asked me again to insert password. I inserted a wrong password and it stores in the cache and I can't change it.
  I tried to uninstall git and no use.
  I deleted from .gitconfig file in user\myUser the lines:</p>
  
  <pre><code>[credential]
  helper = !'C:\\Users\\grin_d\\AppData\\Roaming\\GitCredStore\\git-credential-winstore.exe'
  </code></pre>
  
  <p>The result was that I had to insert again every time the password and username. When I run again: git-credential-winstore it shows me again the wrong password.</p>
  
  <p>Any idea how can I delete the wrong password stored in the cache?</p>