Download latest ViX image for HD51.
If you have a HDD or usb attached then copy the image zip (with e.g. filezilla) to the HDD or US
Then go software management (I think long press blue button) and flash online utility
select STARTUP (I would suggest STARTUP_2 or _3 as ATV will be in STARTUP_1/STARTUP)
select local (you are flashing image zip on HDD/usb)
then select I think device and find where youu copied the zip
highlight and then flash.
ignore saving settings etc
at the end hit exit to return to normal screen
long press Power button
select multiboot
select STARTUP_2 (or_3)
select reboot!!
should reboot to OpenViX
with OpenViX you would do all this with ViX ImageManager.