
You even can`t upgrade your TV with any other, except exact your firmware but lover version.
Only higher versions are accepted by TV. (If your is T-GAP6DEUC -1013, then only T-GAP6DEUC 1014 and older could be installed, not vice versa).
No chance to install firmwares from older models (7 series and above), because TV doesn`t eat it at all.
What is your goal? some functions missing?