Bios flash doesn't recognize .rcv file, Vostro 15 3515

I want to flash bios to the new version. I'm using ubuntu so I have to flash it using .rcv file that I found here

https://www.dell.com/support/home/en-us/drivers/driversdetails?driverid=nvgj3&oscode=ubt20&productcode=vostro-15-3515-laptop

Problem is that file is invisible once I enter bios flas utility. It simply doesn't recognize it. I tried typing name of the file but no luck either. I formatted USB flash to the fat32 as per instructions but doesn't make any difference https://www.dell.com/support/kbdoc/en-us/000124211/dell-bios-updates

Instructions for bios flashing do not match what is on my machine, I don't have option to turn off UEFI boot, or at least I cannot find it...

Really confused. Hope I can get some help.

Thanks.