Here you have the information to convert the model.
1 Connect display, keyboard, mouse and power supply to the N90-HOR and power it Off.
2 Insert the USB Key in one of the USB ports of the N90-HOR.
3 Power On the N90-HOR and press F12 during the boot to enter in the bios boot option.
4 Select the USB option to boot and press enter.
The N90-HOR will boot from USB and start loading the N90-HDX image and licence.
Follow the on screen information up to the message that says to unplug the USB key.
More info about toolkit are here: https://wiki.praim.com/display/PraimToolkit
For any further information they can contact support@praim.com