Hi JHempsey.
Where are you seeing the message "Mac: Command-click Check for Update" exactly?
You can find the Summary tab inside iTunes after you connect your iPhone to your Mac via cable.
If it doesn't automatically appear, click on the phone icon to the right of the Media Kind selector on the top left of the window (under the media controls)

Once you click that, you can find the summary tab on the left, under your device name

Once clicked the Summary tab you can find the button Check for Update on the center of the window, under your iPhone info, to the left of the Restore iPhone... button.
