You can choose the firmware version on this website, the V0.67 is the latest one.
The SD card which is used for upgrading should be FAT32 format.
After downloading the firmware into the SD card, the name of the firmware must be K2. bin, can not be followed by such Numbers as (1) (2).
After the SD card is put into the DVR, it is connected to the power again, and the firmware refresh will start automatically.