Sometimes Canon posts a separate file with the pdf instructions. Look for it on their website. The following is to the best of my memory, so do review the instructions and be sure. Also, I'm on a PC, not a Mac, but I can't imagine there's a lot of difference.
First check your camera's firmware to be sure it needs to be updated.
If the update is newer and you want to install it, download it to your computer and extract it, which it sounds as if you've already done.
Next you need to do a sumcheck... This is to confirm that the fir file size, after you extracted it, exactly matches the size that's noted on the Canon website. If not, you should redo the download. Don't use a fir file that doesn't match. It might cause a failed update and the camera will then probably need to be sent to Canon Service.
After the suncheck, you just need to load the fir file onto a pre-formatted (in the camera) memory card, however you might do that. The easiest way is with a card reader.
Alternatively, you might be able to do the update from the file in your computer, via Canon Utilities.
You just navigate the menu to the firmware notation and click on it (either in the camera itself or in Canon Utilities, after hooking up the camera to the camera via the cable). You'll be asked if you want to update your firmware, click yes.
During the update set the camera aside, don't turn it off and be very careful not to touch any buttons or dials. You don't want to interrupt the update in progress. That can end up with corrupted firmware and your camera will need to be sent to Canon Service.
Be sure your camera is powered up and the battery isn't low. It takes roughly 5 minutes to update and you have to be sure the camera has enough battery charge for that period of time. If the power drops too low and the camera shuts down, the firmware update will be interrupted and corrupted, again needing Canon Service to correct it.
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