Discharge the capacitor. Camera flashes contain very large and powerful capacitors that can stop your heart if you touch them in the right way. It probably won't, but it could. If this scares you, you should probably take it to a professional.

press the "push" button and bend the head 90 degrees into an L shape (not shown in this photo). Remove the rubber cap with "push" embossed on it. It is glued on. I've circled where the holes are in the photo. Insert a resistor in the two holes to discharge the capacitor (also referred to as the condenser). Look up how to discharge a capacitor online if you're not sure.

I skipped this step because I didn't feel like pulling the glue off. You should really discharge the condenser, but if you really don't want to you can minimize the risk by turning the flash on, pressing the "flash" button on the back to mostly discharge it, and turn it of before it has a chance to fully recharge. This minimizes the the risk, but I still got a pretty nasty shock even after doing this. It felt at least as bad a shock from 120VAC from an outlet.