Lightroom 6 standalone

I have Lightroom 6 standalone which i purchased from Amazon in 2015. My laptop recently crashed and i had to reinstall my programs. I downloaded Lightroom but it is at version 6.3 and i need V6.8 to be able to use it with my 5D mark4. 

How can i get it the upgrade to 6.8 without going the subscription route. Also i got a message that say I have used the serial # on the maximum allowed computers and need to deactivate one within 30 days. I only have it on one more computer and am unable to deactivate thie prior download on this computer as the program was lost.

Any thoughts or ideas would be greatly appreciated.