There are several options for installing the firmware. The first option is to install using SD card, the second option is to install without an SD card directly to NAND of the miner using the VNISH TOOLKIT
SD CARD : Download the SD IMAGE , unzip and read manual ( Use SD card to install the firmware (not more than 16gb, FAT 32) Insert the SD card with VNISH FIRMWARE and turn on the asic, if you pull out the SD card the BITMAIN firmware will return. If you need to update the version of vnish firmware which you are already using on the SD card or in NAND you need to download the firmware WEB SD update file and use upgrade function in the firmware.
NAND INSTALL: Download NAND INSTALL IMAGE and VNISH TOOLKIT ( unzip, read manual how to install )