You have to get the firmware updated from a Canon repair centre. I took my 300mm f/2.8 II in and they did it on the on spot in London in about 10 minutes. It was worth the trip. The focussing was a little erratic as I found out in microadjusting the lens previously. But, now it is spot on reproducible. You need it when you are cropping to 700x700 pixels of a small bird about 30 yards away.
5D III, 7D, Powershot SX50, 300/2.8 II, 1.4xTC III, 2xTC III, 70-200/4 IS, 100-400, Sigma 400, 24-105, 15-85, 50/1.8, Sigma 10-20