1. Enter DOS mode
2. Go to the directory where you have placed your newer firmware
3. > ftp IP_address
4. > root
5. > pass
6. > bin
7. > put flash.bin (If the firmware you have gotten is named flash_all.bin, you can rename it to flash.bin)
8. > bye

Wait around 30 seconds for the process to take place
*DO NOT remove the power while upgrading else might cause damage to device