Once upon a time it is needed to upgrade either BIOS or Hard Driver firmware. Since DELL iDRAC 7 does not support writing to .img files anymore since the fw version 1.57.57, there had to be a new way of upgrading the firmware. And the way to do it is via UEFI.
To upgrade BIOS, browse to DELL’s support website for your given server and download the .efi file this way: Select Not Applicable Operating System and expand on the BIOS selection. There, download the .efi file – save in 8.3 format because the UEFI utility can not read longer filenames (as you will see further).
Use any tool which lets you create ISOs and put this .efi file in the .iso. Mount it in a remote console session, enter Boot Manager and follow the screenshots:
Now you are all done. Enjoy your upgraded BIOS 🙂