Having experienced the loss of all my computer software in the past I'm afraid I will lose my LR6 which I downloaded from Amazon on 5/21. I'm concerned because in the future I might not be able to get LR6. I would like to know how I get a copy or back it up some how so that I can access it in the event of a computer crash and it is no longer available
You can download Lightroom anytime from here: Keeping Lightroom Up-to-Date
What you should be concerned about is your serial number - if you loose that, you will have to buy Lightroom again.
You should register your copy of Lightroom with Adobe, once you have done that you can retrieve the number using your Adobe ID. (you should still keep copies of the serial number yourself)