While the tool was originally designed to pull the firmware directly from Apple's website, a change in the file location and name on Apple's part has made it necessary to download & mount the .dmg prior to running the tool.
Double click the firmware file you downloaded in step one to mount the disk image to your desktop.
Right click and select "Open" on the firmware update tool. Since it is not signed with the proper certificate, macOS will likely refuse to open it just by double clicking the file. Right click the file and open from the menu to fix this.
You should have two options in the window - upgrade to 2010 firmware and downgrade to 2009 firmware. Only one option will be available at any given time, dependent on which firmware you have installed.
There is really no reason to ever downgrade to 2009 firmware, as none of those machines are still under any warranty from Apple and the system discs are not as important now that all OS versions are given as software downloads.
You are not required to upgrade your CPUs if you update to the 2010 firmware- your original system configuration will continue to operate as it always has.
Be sure to read any and all information that the utility may pop up.
IF YOU HAVE DIFFICULTY: Try using this alternate tool.
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