I doubt the warranty will be void as it's just a software. Just send it in to service centre and tell them your camera acting funny and go crazy, this will let them have a chance to check and service while at the same time update your camera with the latest firmware available. That happened to me when i last send in for the famous mode dial problem.
As for the firmware, i downloaded when xfusion posted this important post here. Everything is a breeze. Just follow the instruction and voila. Shouldn't have a chance to go wrong unless the battery went low while you update the camera. So just ensure the battery is full charged. This step is mentioned when you are about to update the firmware so relax... follow the steps and you have the latest firmware in your camera.