@ miroslavbl
I guess you are wanting to try a firmware downgrade. I have renewed the link for v5.40 in the firmwares thread as you requested there. To downgrade from microSD you'll need to give v5.40 a higher number than the fw version already running on your unit, e.g. if it's running 6.20 rename 5.40 to 6.21 with RGN_Tool. You will also need to delete the existing GUPDATE.GCD from the unit's .System folder if present or you'll get a continuous loading loop while the sd is inserted.

My advice would be to make a complete copy of the unit's internal memory if you don't have a recent one. I suggest run this command script from a min. size 4GiB sd:

copydir,0:/,1:/BackUp/
reboot

It'll take a while so keep the unit on charge. If you find that GUPDATE.GCD is present on the backup, run this before downgrading the firmware:

del,0:/.System/gupdate.gcd
reboot