I'm trying to find some time to put a fully guide together.
Quick guide below:
1) FTP zip file of chosen image to your storage device, will be something like media/hdd/imagebackups
2) Blue button > ViX > Image Manager > Select the image you want to flash > Press Blue button or OK.
3) You will be prompted to choose a slot. Slot 1 will be your current booting image.
4) Ensure you choose an image that supports Multiboot such as ATV or PLi.
Once flashed, you can switch images by holding down power button on remote > Multiboot > Select slot to boot from.