To Install LR on a second cp do I need to download LR3 then LR5 or can I go right to LR5 also Photoshop cs5 to cs6 extended and Indesign.These are allready purchase in my Personal Manager History?
It isn't necessary to install Lightroom 3. But since you probably purchased Lightroom 5 as an upgrade you will need the Lightroom 3 serial number as well as the new serial number for Lightroom 5.
Adding to what James mentioned, this stands true for both Lightroom and Photoshop. In other words, you don't need to necessarily install the previous versions but while installing the latest versions, in this case Lightroom 5 & PS CS6, you will need the serial keys for previous versions as well along with the current ones.