OK. explain a little more please - Are you wanting to install on new computer? Switch from Windows to MAC?
I want reinstall on same macbook pro I had to wipe my hard drive clean (malware) now i'am reinstalling programs an want to put lightroom back on.
You will need to have your LR 5 license key, if is an upgrade then you will also need an earlier version License key
Download from the link below and install
Insert the LR 5 key and if prompted enter the earlier key.