Steps for downgrade:
- First download 0000 firmware of your need there (available H ones: T-MST14DEUC, T-GFPDEUC, T-GFP8DEUC):
https://mega.nz/#F!SxgEjAiI!cnvb1JXlhvxlsKKRml5K0A
Mirrors:
https://yadi.sk/d/jM_jtM9fmYaB3
https://yadi.sk/d/vzFyDJP7n7rDk
Install it following usual Samsung official procedure for USB upgrade:
How do I upgrade my Samsung TV's firmware via a USB memory drive? - Then repeat upgrade procedure with any other version of your choice. Firmware list you can find here: viewtopic.php?f=70&t=9497#p77431 (check spoiler, donor's access only)