I always used to know these key combinations out of the top of my head, but as the product range increases it is simply to much to remember as you don't update all gear frequently. So this is basically a little cheat sheet for me, but feel free to check it out.
This topic shows all button combinations that are available today, the list will be maintained so should be recently up to date.
You have to hold the buttons during startup to enter update mode.... all other info here
DJ Topics > Pioneer DJ Firmware Update Button Combinations