bios numbering is fairly simple in most cases .numbering is usually a series starting with F1 or firmware 1 (1st version of firmware for a given board)
normally a firmware will only ever go through the set of F numbers ie. f1 f2 f3... sometimes you may be offered an experamental firmware ,for example F3b ,the "b" stands for Beta ,or Pre-release ,once it has been tesed fully the b will be removed .Beta firmwares are usually only offered if a known problem needs addressing and users need a fix quickly , the manufactureres wont simply release any Beta Bios , it will have been tried and tested, but maybe needs more testing before being certified ,you will allways be warned about risk ,when downloading Beta .
Sometimes a motherboard will go through several versions itself , in this case the motherboard will have a verson number ,or "revision number" 1, 1.2. 1.3 etc.
allways make sure you download bios for your revision number only . also when major firmware differences are made that actually change the way hardware works ,you will get different bios names like FA ,or FB etc .
as i am sure you are aware ,your BIOS (basic input output system) is simply a set of instructions that configure your hardware ,and voltages etc immediately before startup . each bios update can be for different needs ,sometimes they address a known bug ,and apply a fix accordingly ,sometimes they do a lot more and allow you to have increased functionality or to enable a new biuld of processor .either way ,its usually a good thing to have the latest bios installed to have complete funcionality and compatability . that said ,if a user is happy with thier motherboard ,and has not installed any hardware that would require an update to work properly ,there is no real need in that case to update .
the old saying , if it aint broke dont fix it , is worth noting .