On March 2012 I purchase a download upgrade LR4. Found out it was not compatible with my old PC OS. Therefore I never got to set it up or use it. I now purchased an New IMAC. Can I download that prog into my Imac or get a LR4 for Imac without having to pay for it gain?
You should be able to use it on either system as long as you install the right version for the system...
Lightroom - all versions