One license covers both. You are permitted two activations and LR is multi-platform.
Thanks for the reply. Am I best to purchase a hard copy disc or a download for LR6?
You can buy from the following link. After clicking "Buy" change from Full to Upgrade; then select your existing LR product from the drop-down menu and the correct pricing will be displayed. Then simply choose “Add to Cart”
It's the only way to get upgrade pricing. You can't buy upgrade disks or downloads anywhere else.