To disconnect from Facebook, you will need to do so through their website, or the Facebook app.

From the Facebook app on your device:
  1. Open the menu (3 horizontal bars)
  2. Select "Settings and Privacy" -> Settings
  3. Select "Apps & Websites"
  4. Select "Logged in with Facebook"
  5. Select the app from the list
  6. Scroll down to "Remove" at the bottom of the page and confirm removal
To remove a game you've connected to Facebook:
  1. Click on the triangle in the top, right-hand corner to show the drop down menu and select "Settings"
  2. 2. Click "Apps & Websites" in the left menu
  3. Select the app and then click the "Remove" button
You may need to close and then open the game to reflect this change and reconnect to Facebook if you choose.