Wireless FW upgrade works and should work. I updated mine using wireless upgrade with my phone.
One thing you need to make sure is that wireless cameras have a good quality wifi signal with the main host wifi base. If the signal is poor or low and if you attempt a FW update, this could cause problems and cause the camera to be come non responsive. The signal needs to be good between the camera and source wifi. When in doubt, put the camera with in 6 feet of the main wifi source before doing any FW updates.
I hope D-Link Brazil will help you out.