I purchased Lr 5.0 in 2013 and upgraded to 5.5 at some point. All my photos are on an external hard drive but how do I get the latest free upgrade of Lr on my new computer that I just purchased. It is a Mac.
You can install Lightroom 5 version on your new machine through this link :
The latest upgrade to Lightroom 6 would not be free. You will have to purchase it if you are willing to upgrade.