I bought Lightroom 6 months ago for my dell laptop and have the CD and serial number and all of that stuff. Now I just got a MacBook Air. Is there a way I can download Lightroom onto my new Mac with using the stuff I have for my dell laptop already? Or do I have to buy Lightroom again for Mac?
After you get your mac up and running using the links in John's post, you need to decide which computer is going to be your primary LR computer since LR is a single-user single-computer system.
See this link for copying the needed files from one machine to another: