Plug it into PC, after 20 seconds; it can enter upgrade mode and both LEDs light. The PC will find device "AT90USB162 DFU", you can download firmware from here and use FLIP to flash it.
If you install the FLIP and install drivers for "AT90USB162 DFU", you can flash HEX files that download from here
and keep the "auto enter upgrade mode" function.
You can flash it with any HEX file, BUT you will lose the "auto enter upgrade mode" function, after this, next time
you have to do a hard upgrade.
We are preparing more detail document for how to do a hard upgrade for PS3YES!.