Small incremental bios ver update is safer than big leap.  Flash bios always has risk.  Do it at your own risk.  You have optiplex 390 motherboard.  There is no great benefit of later bios compared to A03.  The bugs Dell fixed in later bios often has no relevance to you.  Users like to think later bios gives them a better feeling, but often the opposite might happen.  If your 390 is fully working now, weigh the risk of bios update against uncertain benefit.
Hello, so i have bios version A03 motherboard is 0m5dcd and the latest is A14. do i just download A14 and install it or do i have to go 1 by 1 untill A14 for example a03 then a04 then a05 all the way to A14 or theres no need. Also in the BIOS it show A3 but in MSINFORMATION it shows A00 im guessing the bios is the right one ?   
how do i bios update