Take the FX-6350 its much better in gaming than the FX-4300.. The extra cores helps in games like BF4 etc.. 

Newer games nowedeis are more and more optimize for more cores.. more core u have more they will chew.. lol..
Plus its already in most benchmark that FX63xx performs better than the FX43xx in these new games.. lol..

Don't use the term 'heard'.
Newer gen games are using 6 to 8 cores now thanks to PS4/XBO multi core architecture.

Take a look at gamegpu.ru (russian website, it has benchmarks on most recent games with core loading).
Most games on 2014 are utilization 4-6 cores.

EDIT : If you're planning to upgrade from FX4300, jump to FX6300 or FX8320.
The FX6350/8350 are the same version with slightly higher frequencies which can be match easily with FX6300/FX8320 via multiplier adjustment but with more power draw 

if it aint broke, dont fix it.    usually ppl update bios to fix bug(s), increase compatibility (esp for eam/proc) & etc. if u dont need any of those mentioned, leave it. 

updatin of bios can be done via 2 ways usually, windows (tools needed) or in bios (u just need to dl d bin file & save it to ya hdd/usb thumb drive) & go to d bios flashin option.