Hi there,
DFU, Or “Device Firmware Update” is usually a mode you put the hardware in to accept a Firmware update, Sometimes it a menu item and sometimes it’s a button sequence.
I would have a look at the Wiki for the device and see what your choices are. WARNING!!
Sometimes it’s better to see what others who have your device are doing and see if it fits your situation. Lots of Bricks are made by over zealous FOMO users for the latest release.
Start with the WiKi.
HTH
GL 
PJ
