• Download Windows (.exe) version of iDRAC update utility from DELL.
  
• Extract the downloaded .exe file (with 7-zip or something similar).
  
• Go into payload folder where you should will firmimg.d6 file
  
• Login to iDRAC Web GUI and navigate to Remote Access > Update.
• Upload firmimg.d6 file and follow instructions to update the firmware.
  

DELL PowerEdge T310
iDRAC 6