How to change the icon for the Facebook App

To change the icon for the FreeWebstore Facebook app on your Page:
  1. From your  Facebook Page, click to the right of your apps under your cover photo
  2. Hover over the app you want to change the icon for and click
  3. Select Edit Settings from the dropdown menu
  4. Click Change next to Custom Tab Image
  5. On the next screen, hover over the existing image and click Edit
  6. Follow the instructions that appear for uploading a new image


https://www.facebook.com/help/201402119964259