I'm also facing the same issue  I uploaded the new BIOS from DELL web site .exe directly. Run as addminitrator. Wait for the update. Solved.  
I have recently got a BIOS update i.e 1.8.0 to my dell G15 5515 laptop. But I am unable to update it as it always shows BIOS Update Failed as it requires Password so please remove it but i haven't put any kind of password on that . So kindly If any Dell executive seeing then please help me regarding this.[IMAGE]
BIOS Update 1.8.0 Issue