Flashing the BIOS of the Dell PowerEdge C6220 is no simple task. It requires updating the BIOS multiple times in between each step. I highly recommend you have the system on a UPS before you get started.

To get started I make a FreeDOS bootable USB flash drive with RUFUS.
The items you need to download are:

1. Dell C6220 I and II BIOS
2. Dell C6220 BMC 2.25
3. Dell C6220 BMC 2.53

Copy the BIOS exe to a folder on the FLASH drive I named BIOS and renamed to BIOS.
Copy the contents of PEC6220&PEC8000BMC225\Socflash\DOS to BMC223 folder on the flash drive.
Copy the contents of PEC6220IIBMC253\Socflash\DOS to BMC253 folder on the flash drive.

Put each item to the flash drive into its own folder. To make it easier I named each folder BIOS, BMC25, and BMC53 respectively.

1. Flash the BIOS - C:\BIOS\BIOS.exe
2. Delete the BMC logs from with in the BIOS
3. BIOS reset
4. Flash the BMC with 2.25 - C:\BMC223\FBB 1
5. Flash the BIOS - C:\BIOS\BIOS.exe
6. BIOS reset
7. Flash the BMC to 2.53
8. BIOS reset - C:\BMC253\FBB 1
9. Flash the BIOS - C:\BIOS\BIOS.exe
10. BIOS reset

At this point with everything being updated, the BMC is moved to a shared NIC port 1. If you want it separate, there is a BMC option to have sharing disabled in the BIOS.

This method seems to work great. I recommend you flash the NICs after you are done with these steps, but I haven't noticed any performance or compatibility differences.