I guess it is just worded poorly and can be easily misread. It actually says: (64MB or more, 64GB or less)
You can definitely use a 16Gb card for the firmware update as 16Gb is in between 64MB and 64GB.
There are two ways to update the firmware on your camera:
1) Connect the camera to your computer with a USB cable and then use EOS Utility to update the firmware.
2) Use the memory card and copy the file to the "Root" of the memory card. (don't put in in a folder or sub-folder). You will need a memory card reader to transfer the file from your computer to the memory card.
You can. When you download the firmware update, there is a PDF file inside (after you uncompress the zip file). That PDF provides instructions for two different ways to update the firmware.
One method involves connecting the camera to your computer via the USB cable. The other method involves copying the xxxxx.FIR file on the CF card and using the camera menu to perform the firmware update.
I bought a CF card reader for my computer (I use one of these: http://www.amazon.com/Lexar-Dual-Reader-Professional-LRW307URBNA/dp/B007FEFQDA -- that card has both a CF and SD card slot... there's another version which is CF card only (no SD card slot) which is just a few dollars less.)
BTW, part of the reason I use the card reader rather than the USB method is because it's faster. I can import images via the card faster than I can by connecting the camera to the computer over the USB cable.
All good answers, but I didn't see anything regarding the following info....
1. No matter which method you use when updating firmware, you should be sure your camera battery(ies) are fully charged.... you don't want the camera to run out of power in mid-process. That can cause a failed update that "bricks" the camera. I would estimate it takes 3 to 5 minutes to complete a firmware update.
2. There must be a freshly formated memory card in the camera, no matter which method you use. Format the card in the camera, not in your computer. You then can either load (copy) the *.fir file onto the card, or just leave it on your computer and connect the camera to that with the USB cable. (Important note: any images on the memory card will be lost in this process, so make sure you have copied or moved all you want to keep to somewhere safe, such as a folder on your computer.)
Firmware updates are one of the rare times I connect my cameras to the computer with the USB cableI usually don't bother loading the *.fir file onto the camera's memory card. I just tell the camera to use it from the folder on the computer, via the USB. (Note: another time I use the USB is when synching the clocks in multiple cameras, which I do fairly regularly as the clocks get out of sync suprisingly often. Like Tim mentions, I don't use the USB cable to download images from the camera to the computer, that's just too slow. Plus I use multiple cards... sometimes a dozen or more in a day's shoot. So I use a card reader instead.)
It is not hard to do a firmware update... but it is important to do it right. Follow the instructions carefully.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.