Instructions that come with license key say:
“You can register by clicking the HELP button in the top bar and going to GET PREMIUM FEATURES. ”
I figured out the “top bar” meant the menu bar(on Mac), but the drop-down menu under HELP gives several choices. The one I chose, I found out later, gives me this software for one year only instead of “lifetime”. Oh, well…not sure what good M4A files would do me, anyway. ;-) Instructions need to be more concise.