*Most* likely you will not need a bios flash, that CPU has been out for a while now, only when they're first released do you need to flash the bios, if you get the board new, chances are that the stock that needed the bios flash has all ready been sold and the new boards are updated. If you're buying a used board, as the person who owns it if they can flash it for you, a lot of times if it needs the flash they will do it for you.
If you have to flash the bios, Asus makes it really easy. Just look up a set of instructions, follow them, and don't worry too much about it, most of the nightmares about flashing the bios were from years ago. Things have gotten much better over the years.