Dell has an very comfortable way of getting new firmware to nearly all of its server components: The bootable media / ISO or Update CDs. You can find them on this website and very useful. On a basic level, you pick your server, download the ISO, compare the MD5 checksum and burn the ISO onto a DVD. After that, you should get the Servicetag of your server and check for BIOS and iDRAC updates - these should be installed manually first. After that, boot from the DVD and let it install all the needed firmware. Basically, the DVD will cycle through all firmware of components ever installed in the series of your particular server and installs updates if needed. After another reboot, you're done :).
Thanks Dell for being so helpful to your users! 🙂