I downloaded the free trial of Lightroom to my MacBook. Is there anyway I can apply the disc's serial number to my free trial download?
Yes, you type in the serial number into the trial version.
Where do I do that?
When you start the trial version, a screen displays indicating how many days you have remaining in your trial. On that screen is an option to indicate that you have a serial number. Choose that option, and you will be provided with another screen where you can enter the serial number.
Take note that if you downloaded and installed the creative cloud version you will have a different procedure. It will be necessary for you to remove that version and install the trial version from the following website:
Perfect - thanks! I had the cloud version of the free trial, so it wasn't so evident. Thanks for the links to the direct download!