Look for the "EOS Utility" package. Usually, the latest version is labeled EOS Utility 3.x , which is backward compatible with the 5D Mark III.
You cannot update firmware if the camera is in an automatic mode. Turn the dial to "P" (Program) or "M" (Manual) . download eos utility canon 5d mark iii
Follow the on-screen prompts. You may need administrative privileges. Look for the "EOS Utility" package
If you are using a WFT-E7A wireless transmitter, ensure the settings are configured to "PC Connection." download eos utility canon 5d mark iii