Those processors have 2 different sockets (A6-3620 is FM1 and the Athlon 2 series is AM3).
You would have to change your motherboard.
To update a bios go to AMD's website and find the bios download for the CPU you need it for and put it onto a formatted pen drive.
Stick the pen drive with the bios file into the computer you want to update the bios on and boot from it.