It’s the reverse of Importing a .ADM into Group Policy.

Removing ADM Files

  1. Edit the Group Policy
  2. Expand the Policies Folder
  3. Select “Administrative Templates”
  4. In the menu, select “Action”
  5. Select “Add/Remove Templates…”
  6. Highlight the template you want to remove
  7. Click “Remove”, and then click “Close”
  8. Exit the Group Policy Management Editor
  9. Done!