The only way to do it is download 6.1.3/6.1.4 file for your device, DFU restore, and install iOS 6. BUT this cannot be done if Apple stopped signing iOS 6, which they usually do a few hours after a new version launches.
It used to be, but in recent years, Apple shortened the window to a few hours. Don't be surprised if Apple stopped signing iOS 6 at this time.