You can try Platform Specific Bootable ISO to update all firmware component of the server. You can download the same from below link. This is a bootable iso image which carry all firmware. Refer "Installation instructions" section on below link on usage.    
Hello experts and good day,   apologies for the dumb question, but I have worked primarily with Cisco UCS and IBM/Lenovo servers.   I just recently took over the administration of some Dell EMC PowerEdge R640 Servers used as standalone ESXi hosts and I need to apply the latest ESXi security patches as they are running a very old version of VMware ESXi.   Prior to updating ESXi, I would like to update their Firmware in one single step. As the iDRAC does not have external connectivity, is the Smart Bootable ISO created in advance using Dell EMC Repository Manager (DRM) the recommended solution in such scenario ?   Any help will be greatly appreciated.     Thanks and Regards,     Massimiliano
How to properly update Firmware on Dell EMC PowerEdge R640 Servers used as 
standalone ESXi hosts